PURPOSE: To provide the method permitting an observer or a photodetector to surely identify the presence of an object when it reaches the prescribed relative position for the observer or for the photodetector and to provide the distance between two cars confirmation device.

CONSTITUTION: An image hologram 3 installed at the rear of an automobile 1 diffracts the reproduced light on a field of vision 6 backscattering diagonally upward and no light is scattered to an up-and-down area 7 outside the field of vision 6. Therefore, a following car 2 is separated, for example, about 50m or more off, the eyes of a driver 8 who drives the following car are positioned at the area 7 outside the diffracted light beam area 6 and nothing can be seen from the hologram 3. However, when the following car 2 gets closer to about 50m, the eyes of the driver 8 of the following car 2 is within the field of vision 6 and the characters 'STOP' of the hologram 3 can be seen. Then the driver 8 can confirm the distance between two cars is becoming too closer.