PURPOSE: To detect accurately an object with no use of conventional special illumination nor the transmission/reception of a sound wave by using an image sensor.

CONSTITUTION: A sensor area consists of 96 (N=12×8) units of picture elements, and the first screen, i.e., a pattern obtained when a traveling object detecting process is started is read into a CPU4 from an image sensor 2 and stored in the form of the first reference screen. The CPU4 turns off a special flag ALT to cope with the comparatively sudden change of the screen and at the same time sets two counters "SWAPCT" and "LOOPCT" at 0 respectively. Then the CPU4 reads successively the signals given from the sensor 2 as a comparison screen to decide the ON or OFF of the flag ALT and then compares the reference screen with the comparison screen to check the presence or absence of a pattern change.