PURPOSE: To provide a moving object detector for obtaining detection signals with high reliability by preventing the chattering of the detection signals both by the delay of reflected waves due to winds and by re-reflected waves, etc.

CONSTITUTION: An ultrasonic wave transceiver 1 emits ultrasonic waves W1 towards a moving object 3 travelling on a travelling path 4 and receives the reflected waves W2. A transmission part 21 cyclically supplies transmission signals S1 for emitting the ultrasonic waves W1 to the ultrasonic wave transceiver 1 and a reception part 22 performs processing of the reflected waves W1 received by the ultrasonic wave transceiver 1 and outputs reception signals S2. A processing part 23 outputs the moving object detection signals S3 of the 'presence' of the moving object when the reception signals S2 are received within gate time GT set within a period continuously for equal to or more than two periods.