To exactly distinguishing the contents of various reflection wave and detect the existence of the object even in the bad conditions of underground car park which tends to generate multiple reflection wave by detecting the existence of the object based on the detection signal of a sensor.
An ultrasonic transmission timing controller 22 having received reference clock signal of a reference signal clock oscillator 21 oscillating in the transmission circuit side transmits with output timing with non-constant and random transmission wave period to differ the time intervals of transmission output of the ultrasonic detection sensor S. Based on the output timing of varied variable transmission wave, an ultrasonic transmission gate controller 23 amplifies the ultrasonic wave by way of an ultrasonic transmission amplifier circuit 24 and transmits toward a detection region. On the other hand, an ultrasonic reception amplifier circuit 25 amplifies the reflection wave from the detection region and inputs in an ultrasonic reception gate controller 26 for controlling, which is detected by a vehicle detection circuit 27 so as to receive only specific reflection wave with different time intervals, and the existence of a vehicle is judged in a judgment circuit 28.
NAKAMICHI YUJI
OKUBO TATSUYA
