JP2002158772A - Key telephone system and its transfer method in busy state - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a transfer destination in a busy state in advance to each extension terminal. SOLUTION: The key telephone system is provided with a master device 1 and extension terminals 10-14 that are connected to the master device 1 via an extension 60. The master device 1 is provided with an extension terminal interface circuit 2 that extracts digital voice data and control data from the extension terminals 10-14, a time division switch 3, a DTMF sender 4 that transmits a DTMF signal to the extension terminals 10-14 and an external line (not shown in figure), a DTMF receiver 5 that measures a reception level of the DTMF signal received from the extension 60 to provide an output of the detection result of the DTMF signal, a control circuit 6 that controls the entire master device 1, and a memory 7 that stores a table of extension numbers rearranged in the order of higher reception levels. The extension terminals 10-14 are configured with loudspeakers 20-24 that output the DTMF signal and microphones 30-34 that receives the DTMF signal and returns it to the master device 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key telephone apparatus and a busy transfer method thereof, and more particularly, to a key telephone apparatus capable of automatically transferring a busy incoming call to a preset transfer destination and the busy state. Regarding the transfer method.

[0002]

2. Description of the Related Art A conventional example of this kind will be described with reference to the drawings.

FIG. 3 is a system configuration diagram showing an example of a conventional telephone communication system.

In FIG. 3, this conventional example is disclosed in
No. 215239 discloses the contents disclosed in
Is a storage device 112, a control device 113, an exchange unit 11
4 is provided. The storage device 112 stores the position information storage unit 1
12a and a wired telephone storage unit 112b.

The location information storage section 112a stores, for each cordless telephone, the apparatus number, location information indicating the location, and the current call state (whether or not a call is in progress) in association with each other. Also, information indicating whether transfer is performed manually or automatically when an incoming call is received during a call for each cordless telephone is stored. The location information indicates, for example, in which of the wireless areas the cordless telephone is located.

The wired telephone storage unit 12b stores each wireless area and a wired telephone located in the wireless area in association with each other. The control device 113 tracks the current position of each cordless telephone and updates the storage information of the position information storage unit 112a based on the detected position.

When a call arrives at the cordless telephone during a call, the location information and the transfer method are read from the location storage unit 112a, the wired telephone corresponding to the location information is read from the wired telephone storage unit 112b, and the transfer is performed. Transfer the incoming call to the wired telephone using the method.

[0008]

In this prior art, when a call is received by a cordless telephone during a call, the call is transferred to a wired telephone located in the same wireless area as the cordless telephone. Each time the cordless telephone moves and the wireless area changes, the exchange has to update the storage contents of the location information storage unit of the storage device and the storage contents of the wired telephone storage unit.

Therefore, there is a problem that the cordless telephone is not always in the same transfer destination even in the same wireless area as the previous time.

[0010] In the conventional example, the range of radio waves is too wide (usually: line of sight 50 m to 100 m) with wireless communication.
When there are a plurality of wired telephones in one wireless area, it is not specified to which wired terminal the call should be transferred during a call, and there is a problem that the transfer is not always performed to the nearest wired telephone.

For example, the radio waves of a cordless telephone penetrate the walls of a room. Therefore, a busy call may be transferred to a wired phone in another room instead of a wired phone in the same room.

(Object of the Invention) It is an object of the present invention to provide a key telephone apparatus capable of transferring a busy signal to an extension terminal nearest to a busy extension terminal and a busy transfer method thereof.

[0013]

SUMMARY OF THE INVENTION A key telephone apparatus according to the present invention has a main unit connectable to a plurality of external lines, and a plurality of extension terminals each connected to the main unit via an extension. A key telephone device, comprising a mode setting means for setting the key telephone device to the training mode by inputting predetermined information from the extension terminal, and when the main device is set to the training mode, An audible signal transmitting unit that transmits a predetermined audible signal in a predetermined order to a plurality of extension terminals, and all other units except the extension terminal when the audible signal is transmitted from the audible signal transmitting unit. Receiving the audible signal from the extension terminal and receiving the returned audible signal in order, measuring the reception level, and outputting the measured value. Setting means, and the extension terminal of the extension terminal corresponding to the order in which the measured value of the reception level of the reception audible signal is transmitted in a large order in association with the telephone number of the extension terminal at the time of transmitting the audible signal from the audible signal transmission means. Storage means for storing in the order of telephone numbers, and a search result of the storage means as an extension terminal closest to the first extension terminal when there is an incoming call when the first extension terminal among the plurality of extension terminals is busy. Transfer means for transferring the incoming call to the extension terminal that has transmitted the highest reception level associated with the first extension terminal, and wherein the plurality of extension terminals are each audible via the extension. A sounding means for sounding the signal as the reception audible signal, and receiving the reception audible signal from the sounding means from a device other than the extension terminal and transmitting the signal to the main device via the extension. And a reception audio signal sending means for, the audible signal and the received audio signal is the same DTMF signal.

[0014] A busy transfer method for a key telephone apparatus according to the present invention comprises a main device connectable to a plurality of external lines, and a plurality of extension terminals each connected to the main device via an extension. In the key telephone device, the key telephone device is set to a training mode by inputting predetermined information from the extension terminal, and when the training mode is set, the main device is controlled by the audible signal transmitting means to transmit the plurality of extension terminals. An audible signal is transmitted via the extension in a predetermined order with respect to the extension terminal.Next, the extension terminal receiving the audible signal sounds the audible signal as a received audible signal by sounding means, and then, All the extension terminals except the extension terminal at the time of receiving the audible signal receive the reception audible signal from the ringing means from other than the own extension terminal by the reception audible signal sending means. It receives and sends to the main device Te,
Next, the main unit sequentially receives the received audible signals transmitted from all the extension terminals except the extension terminal at the time when the audible signal is transmitted from the audible signal transmission means by the received audible signal level measuring means. Measuring the reception level and outputting a measurement value, and then measuring the reception level of the reception audible signal in association with the telephone number of the extension terminal when the audible signal is transmitted from the main device. The telephone number of the extension terminal corresponding to the order in which the larger value was transmitted is stored by the storage means, and when the first extension terminal of the plurality of extension terminals receives a call while the telephone is busy, the storage means stores the telephone number of the first extension terminal. A second extension terminal that has transmitted the measured value of the highest reception level associated with one extension terminal is searched, and an incoming call to the first extension terminal is transmitted by the transfer means to the second extension terminal. What Feed, the audible signal and the received audio signal is the same DTMF signal.

A key telephone apparatus according to the present invention is a key telephone apparatus comprising: a main device connectable to a plurality of external lines; and a plurality of extension terminals each connected to the main device via an extension. A mode setting means for setting the key telephone device to a training mode by inputting predetermined information from the extension terminal, wherein the main device is set to the training mode, the plurality of extension terminals Starting signal transmitting means for transmitting a starting signal for starting transmission of a radio signal of a predetermined frequency in a predetermined order, and excluding an extension terminal at the time when the transmission of the radio signal is started by the starting signal. Receiving level receiving means for sequentially receiving a measured value of the receiving level at which the wireless signal has been received from all the other extension terminals; and Storage means for storing in the order of the telephone number of the extension terminal corresponding to the order of the largest measured value of the reception level received in association with the telephone number of the extension terminal at the time of transmitting the When the first extension terminal receives a call while talking, the extension terminal that has transmitted the largest measured value of the reception level associated with the first extension terminal from the search result of the storage means as the closest extension terminal when there is an incoming call. Transfer means for transferring the incoming call to the plurality of extension terminals, wherein each of the plurality of extension terminals transmits the radio signal of the predetermined frequency when receiving the activation signal via the extension, A received radio signal that receives the radio signal from the radio signal transmitting means from other than an extension terminal, measures the reception level, and sends the measured value to the main device via the extension And a bell sending means.

A busy transfer method for a key telephone apparatus according to the present invention comprises a main device connectable to a plurality of external lines and a plurality of extension terminals each connected to the main device via an extension. In the key telephone device, the key telephone device is set to a training mode by inputting predetermined information from the extension terminal, and when the training mode is set, the main device is connected to the plurality of extension terminals by a start signal transmitting unit. A start signal for transmitting a radio signal of a predetermined frequency in a predetermined order is transmitted through the extension, and the extension terminal that has received the start signal next receives the start signal, and the extension terminal receives the predetermined signal by radio signal transmitting means. Then, all the extension terminals except the extension terminal at the time when the activation signal is received are transmitted by the radio signals from other than the own extension terminal. The wireless signal by the transmitting means is received by the receiving wireless signal level transmitting means, the reception level is measured, and the measured value is transmitted to the main device via the extension, and then the main device transmits the activation signal. Means for receiving the measurement values sent from all the other extension terminals except for the extension terminal at the time when the start signal is sent by the reception level receiving means, and then sending the start signal from the main unit. Storing the telephone number of the extension terminal corresponding to the order of the largest measured value received in association with the telephone number of the extension terminal at the time of the storage in the storage means, wherein the first extension terminal among the plurality of extension terminals is When there is an incoming call during a call, a search is made from the storage means for a second extension terminal that has transmitted the measured value of the largest reception level associated with the first extension terminal, and The incoming call to the serial first extension terminal and transfers to the second extension terminal.

[0017]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a key telephone apparatus according to a first embodiment of the present invention.

In FIG. 1, a key telephone apparatus according to a first embodiment of the present invention comprises a main device 1 and an extension 60 connected to the main device 1.
And extension terminals 10 to 14 connected via the Internet.

The main unit 1 includes an extension terminal interface circuit 2 for extracting digital voice data and control data from the extension terminals 10 to 14, and a connection destination of the digital voice data for performing an internal call or an external call using a logic circuit. A time-division switch 3 for switching, and a DTMF sender 4 for transmitting a DTMF signal to extension terminals 10 to 14 and an outside line (not shown).
And digital voice data received from the extension 60 and the outside
A DTMF receiver 5 that extracts only the F signal, measures the reception level thereof, and outputs a detection result of the DTMF signal based on a threshold value of the reception sensitivity; a control circuit 6 that controls the entire main device 1; And a clock circuit 8 for storing the current time to the control circuit 6 using an internal counter. The extension terminals 10 to 14 are speakers 20 to 24 for outputting the voice of the hands-free call and the DTMF signal in the present invention, and the microphones for receiving the voice of the hands-free call and the DTMF signal in the present invention and returning to the main device 1. (Microphones) 30 to 34.

In particular, the extension terminal 14 is configured so that various modes can be set for the entire key telephone apparatus by inputting from the ten keys 15.

Next, the operation of the first embodiment will be described with reference to FIG.

The training mode is automatically performed when the key telephone apparatus of the first embodiment is used less frequently, such as during installation work or at midnight.

Next, the training mode will be described.

The training mode is started by the following setting method.

At the time of setting work, the training mode start information is transmitted to the control circuit 6 via the extension terminal interface circuit 2 by a predetermined operation of the ten key 15 of the extension terminal 14, for example, and the control circuit 6 starts the training mode. I do. Alternatively, the control circuit 6 constantly monitors the clock circuit 8, and when a specific time such as midnight occurs, the control circuit 6
Starts the training mode.

When a training mode is set and, for example, a transfer destination when the extension terminal 10 is busy is set, the control circuit 6 controls the DTMF sender 4 to set an arbitrary DTMF.
The control circuit 6 switches the connection destination of the time-division switch 3 so that the speaker 20 of the extension terminal 10
Output the TMF signal.

On the other hand, the extension terminal 11 receives the DTMF signal output from the extension terminal 10 by the microphone 31. The control circuit 6 first controls the time-division switch 3 and sets the DTM
The connection is switched between the F receiver 5 and the extension terminal 11. DT
The MF receiver 5 subjects the received digital audio data to a digital band-pass filter to extract only the DTMF signal, measures the DTMF reception level, and transmits the measured value to the control circuit 6.

Next, the extension terminal 12 and the extension terminal 13 are sequentially
Is performed similarly. That is, each microphone 32 or 33 receives the DTMF signal output from the extension terminal 10. The control circuit 6 controls the time division switch 3 to control the DTMF receiver 5, the extension terminal 12 and the extension terminal 13
Are sequentially switched. The DTMF receiver 5 measures the reception levels of the DTMF signals sequentially received from the extension terminals 12 and 13 and transmits the measured values to the control circuit 6.

The control circuit 6 determines that the DTMF signal output from the extension terminal 10 has the highest reception level.
= “The distance is closest to the extension terminal 10”, the extension numbers are rearranged in descending order of the reception level, and stored in the memory 7 as a “distance table between the extension terminal 10 and each terminal”. By measuring the reception level of the DTMF signal in this manner, the approximate distance from the extension terminal 10 can be grasped.

The above is a method of measuring and judging the order of the distance between the extension terminal 10 and each terminal by measuring the reception level of the DTMF signal of the extension terminals 11, 12, and 13. Similarly, the reception level is stored at the extension terminals other than the DTMF signal output from the extension terminal 11, the extension terminal 12, and the extension terminal 13, and the DTMF signal is output. ,
"Distance table between extension terminal 11 and each terminal", "extension terminal 12
And a distance table between each terminal and a distance table between the extension terminal 13 and each terminal are stored in the memory 7.

Next, the transfer operation during busy time in the first embodiment will be described.

Now, when the extension terminal 13 calls the extension terminal 10 and the extension terminal 10 is busy, a busy tone is normally transmitted from the main device 1 to the extension terminal 13 and the extension call cannot be made.

However, in the main unit 1, since the "distance table between the extension terminal 10 and each terminal" exists in advance in the training mode, the control circuit 6 transmits the extension terminal 1 during the call.
If it is not possible to call 0, the "distance table between the extension terminal 10 and each terminal" stored in the memory 7 is searched,
As a result, the extension terminal 11 closest to the extension terminal 10, for example, the extension terminal 11 can be called.

Next, a key telephone apparatus according to a second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing a key telephone apparatus according to a second embodiment of the present invention.

In the key telephone apparatus of the first embodiment, the reception level of the DTMF signal is measured to grasp the order of the distance from the extension terminal. In the case of the telephone device, the order of the distance from the extension terminal is determined based on the reception level of a wireless signal such as Bluetooth instead of the DTMF signal. First
In the embodiment of the present invention, audible DTMF signal sound is generated to generate noise. However, in the case of the second embodiment, since a radio signal of a predetermined frequency is used, there is no fear of noise. There are no features.

In FIG. 2, the key telephone apparatus according to the second embodiment of the present invention includes a main apparatus 1a and extension terminals 10a to 14a connected to the main apparatus 1a via an extension 60a. The main unit 1a includes an extension terminal interface circuit 2a for extracting digital voice data and control data from the extension terminals 10a to 14a, and a time division for switching a connection destination of the digital voice data by a logic circuit for performing an internal call or an external call. A switch 3a, a control circuit 6a for controlling the entire main unit 1a, a memory 7 for storing an extension number table rearranged by the control circuit 6a in descending order of the reception level, and a control circuit 6a
And a clock circuit 8 for transmitting the information to Extension terminal 10a-
14a is a radio transmission circuit 40-44 for transmitting a radio signal of a specific frequency when a predetermined command is received from the main device 1a, and receives a radio signal transmitted from another extension terminal and sends out a reception level. Wireless receiving circuits 50 to 54
And is configured.

In particular, the extension terminal 14a is configured so that various modes can be set for the entire key telephone apparatus by inputting from the ten keys 15.

Next, a method of setting the training mode of the key telephone apparatus according to the second embodiment will be described because it is the same as that of the first embodiment.

Next, the operation of the second embodiment will be described with reference to FIG. The training mode is automatically performed at the same time as the first embodiment when the key telephone device of the second embodiment is used less frequently, such as during installation work or at midnight.

Next, the training mode will be described.

A training mode is set, for example,
When setting a transfer destination when the extension terminal 10a is busy, the control circuit 6a of the main device 1a sends a predetermined specific frequency to the extension terminal 10a to the extension terminal 10a via the extension terminal interface circuit 2a. Send a command to transmit a wireless signal. The extension terminal 10a that has received this command outputs a radio signal of a specific frequency from the radio transmission circuit 40.

On the other hand, in the extension terminal 11a, when this radio signal is received by the radio reception circuit 51, the reception level is measured, and the measured signal level is transmitted to the main device 1a. In the main device 1a, the control circuit 6a stores the signal level received from the extension terminal 11a in the memory 7 via the extension terminal interface circuit 29.

Thereafter, similarly, the extension terminals 12a and 13a
The control circuit 6a receives and stores the reception level of the radio signal of the specific frequency received from the respective radio reception circuits 52 and 53.

Next, the control circuit 6a changes the reception level of the received radio signal in descending order, and stores "extension terminal 1" in the memory.
0a and each extension terminal ”.

Thereafter, similarly, the main unit 1a sequentially transmits commands to the extension terminals 10a, 12a, and 13a, and the extension terminals 10a and 12 that have not received the command.
The control circuit 6a receives the signal levels of the received wireless signals from the extension terminals 10a and 13a, and stores the "distance table between the extension terminal 11a and each extension terminal" and the "extension" in the memory 7 as in the case of the extension terminal 10a. Distance table between terminal 12a and each extension terminal "
And "distance table between extension terminal 13a and each extension terminal" is stored.

Next, the transfer operation during busy time in the second embodiment is almost the same as that in the first embodiment, and the description is omitted.

[0049]

As described above, the present invention relates to a key telephone having a main unit connectable to a plurality of external lines and a plurality of extension terminals each connected to the main unit via an extension. The apparatus includes mode setting means for setting the key telephone device to the training mode by inputting predetermined information from the extension terminal, and the main device sets a plurality of extension terminals in advance when the training mode is set. Audible signal transmitting means for transmitting a predetermined audible signal in a predetermined order, and receiving and returning audible signals from all the extension terminals except the extension terminal at the time of transmitting the audible signal. A receiving audible signal level measuring means for sequentially receiving the audible signals, measuring the reception level thereof, and outputting the measured values, and associating with the telephone number of the extension terminal at the time of transmitting the audible signal Storage means for storing the order of the telephone number of the extension terminal corresponding to the order in which they were sent a large value of the measured value of the reception level of the received audio signal, a first of the plurality of extension terminals
Transfer means for transferring the incoming call to the extension terminal which has transmitted the highest reception level associated with the first extension terminal from the search result of the storage means as the closest extension terminal when there is an incoming call when the extension terminal is busy Even if the called terminal of the extension terminal is busy, the approximate distance between the busy extension terminal and all other extension terminals in the training mode is grasped and stored in the storage means. Therefore, there is an effect that the call can be transferred to the nearest extension terminal.

Therefore, when there are a plurality of extension terminals in the same room, there is an effect that an emergency response can be promptly made to a busy extension terminal.

Further, since each internal terminal of this key telephone device hardly moves unlike a mobile telephone, information about the distance between extension terminals is once stored in the storage means in the training mode during installation work. With such an arrangement, there is an effect that there is almost no processing for making the change.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a key telephone apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a key telephone apparatus according to a second embodiment of the present invention.

FIG. 3 is a system configuration diagram showing an example of a conventional telephone communication system.

[Explanation of symbols]

1, 1a Main unit 2, 2a Extension terminal interface circuit 3, 3a Time division switch 4 DTMF sender 5 DTMF receiver 6, 6a Control circuit 7 Memory 8 Clock circuit 10, 11, 12, 13, 14 Extension terminals 10a, 11a, 12a , 13a, 14a Extension terminal 15 Numeric keypad 20, 21, 22, 23, 24 Speaker 30, 31, 32, 33, 34 Microphone (microphone) 40, 41, 42, 43 Wireless transmission circuit 50, 51, 52, 53 Wireless reception Circuit 60, 60a extension

Claims (7)

[Claims] 1. A key telephone apparatus comprising: a main device connectable to a plurality of external lines; and a plurality of extension terminals each connected to the main device via an extension. A mode setting unit configured to set the key telephone device to the training mode by inputting predetermined information, wherein the main device is configured to set the training mode to the training mode, and the main device sets a predetermined order for the plurality of extension terminals. An audible signal transmitting means for transmitting a predetermined audible signal, and receiving the audible signal from all other extension terminals except the extension terminal at the time of transmitting the audible signal from the audible signal transmitting means. Received audible signals that have been returned are sequentially received and their reception levels are measured, and the received audible signal level measurement means for outputting the measured value; and Storage means for storing, in correspondence with the telephone number of the extension terminal at the time of transmitting the audio signal, the telephone number of the extension terminal corresponding to the order in which the measured value of the reception level of the reception audible signal is transmitted in the order of larger value; When a first extension terminal out of the plurality of extension terminals receives a call when the terminal is busy, the first extension terminal is associated with the first extension terminal from the search result of the storage means as the extension terminal closest to the first extension terminal. And a transfer means for transferring the incoming call to the extension terminal which has transmitted the highest reception level. 2. A plurality of extension terminals each receiving the audible signal via the extension and sounding the sound as the reception audible signal, and the reception audible signal by the sounding means other than the extension terminal. 2. A key telephone apparatus according to claim 1, further comprising: a reception audible signal transmitting unit for receiving the audible signal and transmitting the audible signal to the main apparatus via the extension. 3. A key telephone apparatus comprising: a main device connectable to a plurality of external lines; and a plurality of extension terminals each connected to the main device via an extension. The key telephone device is set to a training mode by inputting the received information, and when the training mode is set, the main device sends audible signals in a predetermined order to the plurality of extension terminals by audible signal transmitting means. Is transmitted through the extension, and then the extension terminal that has received the audible signal sounds the audible signal as a reception audible signal by sounding means, and then removes the extension terminal at the time of receiving the audible signal. All the extension terminals receive the reception audible signal by the ringing means from other than the self extension terminal by the reception audible signal transmission means and transmit it to the main device, The main unit receives the received audible signals transmitted from all the extension terminals except for the extension terminal at the time when the audible signal is transmitted from the audible signal transmission means, and sequentially receives the received audible signals transmitted from the reception audible signal level measurement means. The reception level is measured and a measurement value is output, and then the measurement value of the reception level of the reception audible signal is larger in association with the telephone number of the extension terminal at the time of transmitting the audible signal from the main device The telephone numbers of the extension terminals corresponding to the order in which the values are sent are stored by the storage means, and when the first extension terminal among the plurality of extension terminals receives a call when the telephone is busy,
A second transmitting the measured value of the highest reception level associated with the first extension terminal from the storage means;
A busy transfer method for a key telephone device, characterized by retrieving an extension terminal of (1) and transferring an incoming call to said first extension terminal to said second extension terminal by a transfer means. 4. The key telephone apparatus according to claim 1, wherein said audible signal and said received audible signal are the same DTMF signal. 5. A key telephone apparatus comprising: a main device connectable to a plurality of external lines; and a plurality of extension terminals each connected to the main device via an extension. A mode setting unit configured to set the key telephone device to the training mode by inputting predetermined information, wherein the main device is configured to set the training mode to the training mode, and the main device sets a predetermined order for the plurality of extension terminals. Starting signal transmitting means for transmitting a starting signal for starting transmission of a radio signal having a predetermined frequency, and all other extensions except the extension terminal at the time when the transmission of the radio signal is started by the starting signal. A reception level receiving means for sequentially receiving a measurement value of a reception level at which the radio signal has been received from a terminal; Storage means for storing in the order of the telephone number of the extension terminal corresponding to the larger value of the measured value of the reception level received in association with the telephone number of the first extension terminal; When there is an incoming call during the transfer, the incoming call is transferred to the extension terminal that has transmitted the largest reception level measurement value associated with the first extension terminal from the search result of the storage means as the closest extension terminal. And a key telephone device. 6. A radio signal transmitting means for transmitting the radio signal of the predetermined frequency when each of the plurality of extension terminals receives the activation signal via the extension, and the radio signal from a device other than the self extension terminal. 6. A receiving radio signal level transmitting means for receiving the radio signal from the transmitting means, measuring the reception level thereof, and transmitting the measured value to the main unit via the extension. Button telephone device as described. 7. A key telephone apparatus comprising: a main device connectable to a plurality of external lines; and a plurality of extension terminals each connected to the main device via an extension. The key telephone device is set to the training mode by inputting the received information, and when the training mode is set, the main device is set in advance in a predetermined order to the plurality of extension terminals by the activation signal transmitting means. A start signal for transmitting a radio signal of the predetermined frequency is transmitted through the extension, and the extension terminal that has received the start signal transmits a radio signal of the predetermined frequency by radio signal transmitting means, All the extension terminals except the extension terminal at the time of receiving the activation signal receive and receive the radio signal from the radio signal transmission means from other than the self extension terminal. And the measured level is sent to the main unit via the extension, and then the main unit sends the start signal by the start signal sending unit. Except for the extension terminals, the measurement values sent from all other extension terminals are sequentially received by the reception level receiving means,
Next, storing the telephone number of the extension terminal corresponding to the order of the largest measured value received in association with the telephone number of the extension terminal at the time of sending the activation signal from the main device in the storage means, When a first extension terminal among the extension terminals receives an incoming call during a call, the second extension unit sends the measured value of the highest reception level associated with the first extension terminal from the storage unit. A busy transfer method for a key telephone device, characterized by retrieving an extension terminal of (1) and transferring an incoming call to said first extension terminal to said second extension terminal by a transfer means.