JPH06317670A - Inter-vehicle distance measuring device - Google Patents

Abstract

PURPOSE:To provide an inter-vehicle distance measuring device simple in constitution and short in the inter-vehicle distance computing time without using a manual means such as eye-estimation. CONSTITUTION:A laser beam transmitting means 3 andalaserbeam receiving means 4 fitted to both sides of the front face of an own vehicle 1 are operated while being swept by a sweeping means 5. Laser beams are radiated on the front face of the vehicle while being swept, and the inter-vehicle distance to a preceding vehicle 2 is computed from angles in the existing direction of reflectors 6A, 6B fitted to the preceding vehicle 2 and the spacing of the reflectors 6A, 6B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an inter-vehicle distance measuring device for measuring the distance between moving bodies such as automobiles traveling on a road.

[0002]

2. Description of the Related Art At present, a moving body (mainly an automobile) measures a distance between a moving body and a moving body which a driver travels immediately in front of the moving body, and measures a distance between the vehicles so that the driver, that is, a person's will does not have a risk of collision. Is running. However, in this case, for example, when the driver is tired due to lack of sleep, he / she makes a mistake in the visual measurement and cannot maintain an accurate inter-vehicle distance, so the moving body collides.

Further, if an attempt is made to secure a vehicle-to-vehicle distance by visual inspection, the accuracy of the vehicle-to-vehicle distance is poor because it is a visual observation, and the utilization rate of the road is poor because the vehicle-to-vehicle distance must be maintained more than necessary. Therefore, a highly accurate, highly reliable and inexpensive inter-vehicle distance measuring device has been demanded. FIG. 7 shows a conventional inter-vehicle distance measuring device described in, for example, Japanese Patent Laid-Open No. 1-253100. As shown in the figure, 71 is a switch section,
Reference numeral 72 is a control circuit unit, 73 is a slit light projecting unit, and 74 is a speedometer, which is detected in advance by the speedometer 74 by operating the switch unit 71 when the driver wants to know the distance to the preceding vehicle. The slit light is projected from the slit light projection means 73 onto the road at the vehicle front distance determined by the control circuit unit 72 according to the traveling speed of the vehicle, and the driver himself / herself confirms the projected slit light to determine the inter-vehicle distance. to decide.

FIG. 8 shows another conventional example. In the figure, 81 is a vehicle speed detection means, 82 is a slit light projection means, 8
Reference numeral 3 denotes a video camera, which captures an image of a road region including the slit light projected by the video camera 83, and calculates the presence or absence of a preceding vehicle and an obstacle and the distance to the preceding vehicle by image processing from the captured image. It has become.

[0005]

However, in the above-mentioned device, the device must be operated by the driver's own operation, and the safety must be confirmed by the driver himself. It was not a valid safety confirmation method.

In addition, since the driver is a human being, and because he is a human being, for example, due to carelessness during driving, there are many cases in which the distance between the vehicles cannot be secured and an accident occurs.

Further, in the method of capturing a scene in front of a moving body with a video camera and calculating the inter-vehicle distance by image processing, the processing speed of the image processing is limited, and there is a problem in reliability during high-speed traveling. It was

An object of the present invention is to solve the above problems and to provide an inter-vehicle distance measuring device capable of notifying a driver of a danger ahead of a vehicle by providing the device itself with a danger judging function. .

[0009]

In order to achieve the above object, the present invention provides a laser light transmitting means for emitting a laser light substantially forward of a vehicle, a sweeping means for sweeping the laser light, and the laser light transmitting means. Of the laser light emitted by the means, the laser light receiving means for receiving the laser light reflected and returned by the reflector attached to the rear part of the preceding vehicle, and the arrival of the signal received by the laser light receiving means Angle detecting means for detecting the angle at which the reflector exists from the direction, and an inter-vehicle distance for calculating the inter-vehicle distance from the preceding vehicle from the angle detected by the angle detecting means and the distance between the reflector and the reflector stored in advance in the memory. An inter-vehicle distance measuring device comprising a calculating means, wherein the laser light transmitting means and the receiving means are arranged at substantially the same position.

Further, a laser beam transmitting means for emitting a laser beam substantially forward of the vehicle, a sweeping means for sweeping the laser beam, and a laser beam emitted by the laser beam transmitting means are emitted to the rear of the preceding vehicle. Laser light receiving means for receiving the laser light reflected back to the attached reflector, and angle detecting means for detecting the angle at which the reflector exists from the arrival direction of the signal received by the laser light receiving means. And two inter-vehicle distance calculating means for calculating the inter-vehicle distance from the preceding vehicle from the angle detected by each of the two angle detecting means and the distance between the two laser light transmitting means stored in advance in the memory,
The inter-vehicle distance measuring device is characterized in that the two laser light transmitting means, the receiving means, and the sweeping means are arranged at both ends of the front surface of the vehicle.

Further, the inter-vehicle distance calculating means is an inter-vehicle distance measuring device characterized by calculating the inter-vehicle distance with the preceding vehicle only when the preceding vehicle is substantially in front of the own vehicle, and modulates the laser light to be transmitted. It is an inter-vehicle distance measuring device characterized in that a modulator is provided.

Further, the distance calculating means is an inter-vehicle distance measuring device characterized by including a vehicle type selecting section for determining the vehicle type of the preceding vehicle, and storing the respective vehicle widths for each vehicle type.
Further, the vehicle type selection unit is an inter-vehicle distance measuring device characterized by selecting a preceding vehicle from the state of a reflector attached to the preceding vehicle.

[0013]

According to the present invention having the above-described structure, the laser beam is emitted toward the preceding vehicle, and the direction in which the reflector is present is reflected from the laser beam reflected and returned by the reflector attached to the rear portion of the preceding vehicle. Is detected and the inter-vehicle distance is measured from the directions and the intervals.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view of the basic principle of an inter-vehicle distance measuring apparatus according to the first embodiment of the present invention. In the figure, reference numeral 1 denotes a vehicle, which is a vehicle (following vehicle) here. 2 is a preceding vehicle of the vehicle 1. Reference numeral 3 denotes a laser light transmitting means installed on the front surface of the vehicle 1, which is composed of a semiconductor laser element and a cylindrical lens. Reference numeral 4 denotes a laser light receiving means for receiving the laser light returned from the reflectors 6A and 6B attached to the preceding vehicle 2 among the laser light transmitted from the laser light transmitting means 3. The laser light receiving means 4 is attached at substantially the same position as the laser light transmitting means 3. Reference numeral 5 is a sweeping means for sweeping the laser transmitting direction. In this embodiment, a DC motor is used to sweep a certain range in front of the vehicle 1 in a certain direction at a certain speed. Note that a stepping motor may be used as the sweeping means 5, and in this case, the driving circuit can easily reverse it, so that the sweeping may be performed to the left and right. 6
A and 6B are light reflectors provided on the left and right of the rear part of the preceding vehicle 2, and reflect the transmitted laser light in the same direction as the emitted direction. In this embodiment, a commonly used delineator is used. 7 is a reception angle detection means,
The arrival direction of the laser light received by the laser light receiving means 4 is detected. In the present embodiment, the receiving angle detecting means 7 is composed of a microcomputer, and the program detects the receiving angle of the laser light from the timing of driving the laser light receiving means 4 and the sweeping means 5. The sweeping means 5 may be provided with an encoder and the output of this encoder may be used to detect the reception angle.
Reference numeral 8 denotes a distance calculation means, which is the angle information obtained by the reception angle detection means 7 and the reflector 6A previously stored in the memory.
And the distance L between 6B and the like, the inter-vehicle distance between the preceding vehicle 2 and the own vehicle 1 is calculated. Reference numeral 9 denotes a modulator, so that the laser beam transmitted by the laser beam transmitting means 3 can be distinguished from noise such as a signal emitted from another vehicle or ambient illumination light,
Modulates laser light into pulse code.

Next, the operation principle of this embodiment will be described. When the transmitting direction of the laser light is changed by the sweeping means 5, the reflected light is reflected on the laser light receiving means 4 only when the transmitting direction of the laser light transmitting means 3 is exactly the direction of the reflector 6A and the reflector 6B. Be received. Vehicle 1 at this time
The angle α and β between the traveling direction (indicated by S in FIG. 1) and the light transmitting direction (which is also the receiving direction) are detected by the transmission / reception angle detecting means 7. Reflector 6A and reflector 6B are typically
They are provided at almost both ends of the vehicle, and although there are some differences in the size and mounting position of the vehicle, they can be regarded as substantially constant intervals. Assuming that this interval is L, the distance calculation means 9 obtains the following values from the values of the angles α and β.

As shown in FIG. 2, the angle θ (vehicle 1 and preceding vehicle 2
Angle of inclination), L, L ₀ , angle γ and angle δ,

[0018]

[Equation 1]

[0019]

[Equation 2]

[0020]

[Equation 3]

However,

[0022]

[Equation 4]

Substituting (Equation 4) into (Equation 1)

[0024]

[Equation 5]

Since θ is considered to be substantially zero when the vehicle is traveling on a normal road, it is assumed that L≈L _0, and (Equation 5) is

[0026]

[Equation 6]

[0027] Therefore, given L,
X is obtained by measuring the values of the angle α and the angle β.

As shown in FIG. 1, the preceding vehicle 2 is the own vehicle 1
Since θ is considered to be zero when the vehicle 2 is substantially in front of the vehicle 1, the inter-vehicle distance to the preceding vehicle may be measured only when the vehicle 2 is in front of the host vehicle 1.

As described above, the value of L is slightly different depending on the size of the preceding vehicle and the mounting position of the reflector. Therefore, if L is the smallest value among the existing ones, It is safe because the calculated inter-vehicle distance x is also the minimum.

Further, by restricting the value of L to be constant regardless of the vehicle type, it is not necessary to estimate the value of L, and accurate distance measurement can be performed.

Next, the operation of the embodiment will be described. First, in order to emit a laser beam to the preceding vehicle 2, the sweeping means 5 is set to the initial setting position. In this embodiment, the sweeping means 5 has a left side of 30 degrees and a right side of 3 with respect to the traveling direction S.
Since it is designed to sweep in the range of 0 degree, 30 to the left
The degree position is the initial value. Next, the laser beam transmitting means 3 emits a laser beam. This laser beam is modulated into a pulse code or the like by the modulator 9 so that it can be distinguished from a signal emitted from another vehicle or noise such as surrounding illumination light, and has a signal unique to each vehicle. Next, the transmitting / receiving means 3 is swept by the sweeping means 5 while emitting a laser beam, and the preceding vehicle 2 is searched. If the preceding vehicle 2 is within the search range, the reflector 6A of the preceding vehicle 2
The laser beam reflected by the laser beams 6 and 6B is received by the laser beam receiving means 4. When the laser beam receiving means 4 receives the laser beam, the reception angle detecting means 7 stores the direction α of the reflector 6A in the memory of the distance calculating means at the timing. Next, the sweeping means 5 continues the search, and the direction β of the reflector 6B is detected in the same manner as above. Here, the distance calculation means 8 calculates the inter-vehicle distance x from the preceding vehicle from the angles α and β previously stored in the memory and the previously stored value of L using the above mathematical formula. By displaying the calculated inter-vehicle distance x on the monitor at the driver's seat, the inter-vehicle distance with the preceding vehicle 2 can be accurately known.

The sweeping speed of the sweeping means 5 is 120 degrees / second in this embodiment, and the sweeping speed is 60 degrees, but the sweeping speed may not be constant. For example, the sweep speed may be increased in association with the vehicle speed so that the vehicle speed increases. Regarding the sweep angle, in the present embodiment, the sweep was performed in the range of 60 degrees, which is 30 degrees to the left and right, but this is not fixed to a constant angle either.
For example, the sweep angle may be narrowed as the speed increases. Further, this sweep angle may be interlocked with the steering angle of the steering wheel to increase the sweep angle when the vehicle is in a turning state or a lane change state. Further, this sweep angle can be made small by tracking the preceding vehicle once the preceding vehicle is detected.

In this embodiment, the sweeping means 5 sweeps only in the horizontal direction, and the laser light transmitting means 3 uses a cylindrical lens as one of the constituent elements and transmits the laser light with a certain width. Therefore, we have overcome the positional deviation of the reflector due to the difference in vehicle height of the preceding vehicle, but without using this cylindrical lens, for example, by combining vertical sweep with this horizontal sweep, the vehicle height can be increased. It is possible to irradiate a laser beam on a reflector of a large car or the like, which is very different from other cars.

In this case, since the cylindrical lens is not used, the output of the laser light can be utilized to the maximum.

Further, in this embodiment, the laser light is used for the inter-vehicle distance measurement, but light such as visible light, infrared light, far infrared light, and ultraviolet light can be used instead of the laser light.
It is easy to realize that these lights can be switched and used depending on the surrounding conditions. Therefore, in these cases, a semiconductor laser element or a light emitting element such as various LEDs can be used as the light source.

The sweeping means 5 is constructed by arranging these light sources in a line or in an arc shape and sequentially lighting them.
It is also possible to omit. Further, by adopting such a configuration, the incident angle at that time can be specified from the lighting sequence and the lighting place, so that the receiving angle detecting means such as an encoder can be omitted.

Further, in the present embodiment, the calculated inter-vehicle distance is displayed on the monitor in the driver's seat and the driver himself / herself judges whether or not there is a danger. However, for example, when the inter-vehicle distance becomes a certain value or less, When a vehicle is judged to be in a dangerous state, a warning state is given or a lamp is turned on if a dangerous state judging means is provided to judge the dangerous state from changes in vehicle distance, vehicle speed, etc. It may be turned on to warn the danger signal. Alternatively, when the vehicle is in a dangerous state, the braking device or the steering device may be operated to avoid the dangerous state.

As described above, according to this embodiment, the laser beam is emitted to the reflector of the preceding vehicle, and the angle α of the direction of the reflector is set.
Since the vehicle-to-vehicle distance is calculated from the distance L between β and β and the reflector, the vehicle-to-vehicle distance can be measured with a much higher accuracy than that of the conventional visual measurement.

Further, since the inter-vehicle distance is calculated from the angle at which the reflectors exist and the distance between the reflectors, the distance to the preceding vehicle can be calculated without using the propagation speed of radio waves or sound waves, so the calculation process is simple. And the circuit itself becomes simple. In addition, it does not require a huge amount of processing as in the case of using image processing, and the calculation time of the inter-vehicle distance is extremely short, which is useful for avoiding a collision accident between vehicles, particularly a collision accident during high-speed traveling.

Next, a second embodiment of the present invention will be described. In this embodiment, if the preceding vehicle 2 is, for example, a motorcycle or the like and is provided with only one reflector, the distance cannot be measured by the method of the above-mentioned embodiment, so that this problem is solved. Is.

In FIG. 3, reference numeral 6 is a reflector attached to the rear portion of the preceding vehicle 2. In this embodiment, the preceding vehicle 2 has only one reflector such as a motorcycle. Reference numeral 3 denotes a laser light transmitting means, and in the present embodiment, two transmitting means are used, each of which is attached to both sides of the front surface of the vehicle 1. The laser beam receiving means 4, the sweeping means 5, the receiving angle detecting means 7 and the modulator 9 are also provided in the same manner as the transmitting / receiving means 3 and are respectively attached to both sides of the front surface of the vehicle 1. Distance calculation means 8
Is the same as that of the first embodiment. The distance calculating means 8 calculates the distance to the preceding vehicle from the angles detected by the left and right receiving angle detecting means 7 and the value of L stored in the memory. Further, the laser light transmitting means 3, the laser light transmitting means 4, the sweeping means 5, the reception angle detecting means 7, and the modulator 9, which are provided two by two, operate independently of each other. The modulator 9 may be configured as one and shared by the left and right transmitting means 3.

Next, the operation of this embodiment will be described. Example 1
The same operation as above is independently performed using the laser light transmitting means 3, the laser light receiving means 4, the sweeping means 5, the reception angle detecting means 7, and the modulating means 9 on the right and left sides.
However, what is different from the first embodiment is the sweep direction of the sweep means 5. In this embodiment, the left sweeping means 5 first starts sweeping from the front left 30 ° direction, while the right sweeping means 5 initially starts sweeping from the right 30 ° direction. Further, the sweeping directions of the left and right sweeping means are reversed.

While sweeping, the reflectors 6 attached to the preceding vehicle 2 are searched in the same manner as in the first embodiment to detect the angles α and β shown in FIG.

Once α and β are obtained, the following equation is obtained as in the first embodiment.

[0045]

[Equation 7]

Then, the inter-vehicle distance x is obtained. The operation after this is the same as that of the first embodiment, and is omitted here.

Next, a method of detecting the preceding vehicle 2 having a certain width beside the automobile or the like in the embodiment will be described.

FIG. 4 is a schematic view assuming that the preceding vehicle 2 is an automobile in the embodiment.

As shown in the figure, when the preceding vehicle 2 is an automobile, first, the laser light transmitting means 3, the laser light receiving means 4, the sweeping means 5 and the receiving angle detecting means 7 arranged on the left and right sides make the angle α ₁ , Four angles of angle α ₂ , angle β ₁ and angle β ₂ are detected.

Using the values of these four angles and the distance L ₁ between the laser light transmitting means 3, the inter-vehicle distances x ₁ and x ₂ are obtained by the following equations.

[0051]

[Equation 8]

[0052]

[Equation 9]

The inter-vehicle distances x ₁ and x ₂ thus obtained are compared and the smaller one may be adopted as the inter-vehicle distance.

In this case, the reflector 6A of the preceding vehicle 2
Even if the distance L between the reflector and the reflector 6B is not known, the inter-vehicle distance can be accurately obtained. That is, the reflector 6A and the reflector 6
The distance to B can be obtained separately. However, in this case, the angles α ₁ and α ₂ or the angles β ₁ and β ₂ must be obtained at the same time. Since the own vehicle 1 and the preceding vehicle 2 are both traveling and their positional relationship and distance are constantly changing, there is a difference in the measurement time between the angle α ₁ and the angle α ₂ , or between the angle β ₁ and the angle β _2. And an error occurs in the calculated value of x ₁ or x ₂ . In order to eliminate this error, for example, once the reflector 6A and the reflector 6B are detected once as described above, they are always tracked, the sampling interval is shortened, and the measurement interval of each angle is narrowed as much as possible. I should do it.

[0055] The receiving angle detecting means 7, as shown in FIG. 5, the light receiving element 12 ₁ in a semi-circular, _12-2 ..... 12
_{-With n} arranged (a line sensor arranged in a semicircle can also be used.

As described above, according to the present embodiment, the laser light transmitting means 3, the laser light receiving means 4, the sweeping means 5, the transmission / reception angle detecting means 7 and the modulator 9 are provided two by two, and these are installed in the vehicle 1.
Even if the preceding vehicle is a single vehicle or the like, it is possible to detect the inter-vehicle distance without error by attaching both sides of the front surface of the vehicle.

Further, since the distance L between the reflector 6A and the reflector 6B of the preceding vehicle is not used in the calculation of the inter-vehicle distance, it is not necessary to replace the value of L with the estimated value, and the inter-vehicle distance can be measured more accurately. be able to.

Next, a third embodiment of the present invention will be described. This embodiment is the same as the preceding vehicle 2 in the first embodiment.
The purpose is to accurately estimate the distance L between the reflectors 6A and 6B attached to the.

In order to achieve the above object, the present embodiment has the following features.
This is a reflector with a modified shape and mounting method.

FIG. 6 shows a method of mounting the reflector in this embodiment. As shown in the same figure, according to the size of the vehicle, it is classified into four stages, the attachment method of the reflector corresponding to each rank is determined, and the reflector is attached according to the attachment method.

In this embodiment, as the reflector, a normal reflector is prepared, and the reflectors are classified into four ranks according to the number of the reflectors attached and the difference between the left and right.

Then, the number of reflectors and the mounting method corresponding to each rank are determined.

In the case of car type 1 (large freight car), four reflectors are prepared, and two reflectors are attached to each of the left and right sides. Leave at least 5 to 10 cm between the attachments.

In the case of vehicle type 2 (large passenger car), three reflectors are prepared, one reflector is installed on the left side of the rear part and two reflectors are installed on the right side of the rear part.

In the case of car type 3 (normal passenger car), three reflectors are prepared, and two reflectors are prepared in the case of car type 4 (light vehicle) in which two reflectors are mounted on the left rear side and one reflector is mounted on the rear right side. Then, install one on each side.

The method of mounting the reflector is determined as described above, and the distance calculation means 8 stores L, which is a constant necessary for calculating the inter-vehicle distance, in four stages as in the above agreement.

The distance calculating means 8 detects the direction in which the reflector 6 exists based on the output from the receiving angle detecting means 7, determines the state in which the appreciation device is attached, and the state in which the reflector is attached. Then, the vehicle type is determined such as whether the preceding vehicle is a large vehicle or a light vehicle, and the inter-vehicle distance is calculated using the vehicle width L corresponding to the vehicle type.

Also in this case, if the value of L is regulated by law for each vehicle type, an accurate distance can be measured.

The other operations are the same as those in the first embodiment, and are omitted here.

In the present embodiment, the maximum number of reflectors is limited to four, but it is possible to further increase the rank of each vehicle type by increasing the number of reflectors.

Also, the rank of each vehicle type can be increased by changing the mounting method of the reflector and the mounting method of the left and right.

Furthermore, several types of reflector shapes are prepared,
The vehicle type may be selected based on this difference in shape.

Further, this reflector may be attached during the automobile manufacturing process, or only this reflector may be sold separately and the owner of the automobile may attach it according to the standard. Good.

Further, this reflector may be of a seal type. As described above, according to the present embodiment, the shape and number of reflectors attached to the preceding vehicle can be devised to rank the vehicles according to vehicle type, and the vehicle width of the preceding vehicle can be accurately measured. The error in the calculation process can be minimized, which has a great effect on safer and more accurate control.

[0075]

As described above, according to the present invention, a reflector such as a laser beam is applied to the reflector at the rear of the preceding vehicle, the direction in which the reflector is present is detected, and this angle and the gap between the reflectors are detected. Therefore, since the inter-vehicle distance is measured, the inter-vehicle distance can be obtained more accurately and more accurately than in the conventional case where the inter-vehicle distance is calculated by visual observation. In addition, by providing two laser light irradiation units on the vehicle and independently obtaining the angles at which the reflectors of the preceding vehicle are present, the
For a preceding vehicle with only one reflector,
The inter-vehicle distance can be accurately obtained.

Further, by devising the shape and mounting method of the reflector, the vehicle width of the preceding vehicle can be classified and stored, and the error in the inter-vehicle distance calculation can be minimized.

Further, by providing the device itself with a danger judging function, it is possible to notify the driver of a danger ahead of the vehicle.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic principle of an inter-vehicle distance measuring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a basic principle of an inter-vehicle distance measuring device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a basic principle of an inter-vehicle distance measuring device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a basic principle of an inter-vehicle distance measuring device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an example of a configuration of a light receiving section in the second embodiment of the present invention.

FIG. 6 is a vehicle width L of a preceding vehicle in the third embodiment of the present invention.
Illustration of rank classification

FIG. 7 is a block configuration diagram of a conventional inter-vehicle distance measuring device.

FIG. 8 is a block configuration diagram of a conventional inter-vehicle distance measuring device.

[Explanation of symbols]

 1 vehicle 2 preceding vehicle 3 laser light transmitting means 4 laser light receiving means 5 sweeping means 6A reflector 6B reflector 7 reception angle detecting means 8 distance calculating means 9 modulator

Claims (6)

[Claims] 1. A laser light transmitting means for emitting a laser light substantially forward of a vehicle, a sweeping means for sweeping the laser light, and a rear portion of a preceding vehicle of the laser light emitted by the laser light transmitting means. Laser light receiving means for respectively receiving the laser light reflected and returned by the two reflectors attached to the reflector, and detecting the angle at which the reflector exists from the arrival direction of the signal received by the laser light receiving means. The laser light transmission includes an angle detection means and an inter-vehicle distance calculation means for calculating an inter-vehicle distance from a preceding vehicle from an angle detected by the angle detecting means and a distance between two reflectors of the preceding vehicle stored in a memory in advance. An inter-vehicle distance measuring device, characterized in that the means and the receiving means are arranged at substantially the same position. 2. A laser beam transmitting means for emitting a laser beam substantially forward of the vehicle, a sweeping means for sweeping the laser beam, and a rear portion of the preceding vehicle among the laser beams emitted by the laser beam transmitting means. Laser light receiving means for receiving the laser light reflected back by the reflector attached to the reflector, and angle detecting means for detecting the angle at which the reflector exists from the arrival direction of the signal received by the laser light receiving means. And a vehicle-to-vehicle distance calculating means for calculating the vehicle-to-vehicle distance from the preceding vehicle from the angle detected by each of the two angle detecting means and the distance between the two laser light transmitting means stored in advance in the memory. An inter-vehicle distance measuring device characterized in that the two laser light transmitting means, the receiving means, and the sweeping means are arranged at positions on both ends of a front surface of a vehicle. 3. The inter-vehicle distance measuring device according to claim 1, wherein the inter-vehicle distance calculating means calculates the inter-vehicle distance with the preceding vehicle only when the preceding vehicle is substantially in front of the own vehicle. 4. The inter-vehicle distance measuring device according to claim 1, further comprising a modulator for modulating the laser light to be transmitted. 5. The inter-vehicle distance according to any one of claims 1 to 4, wherein the distance calculation means includes a vehicle type selection unit for determining the vehicle type of the preceding vehicle, and stores the vehicle width of each vehicle type. Distance measuring device. 6. The inter-vehicle distance measuring device according to claim 5, wherein the vehicle type selection unit selects the preceding vehicle from the state of the reflector attached to the preceding vehicle.