METHOD AND DEVICE FOR DETECTING MOVING OBJECT

PROBLEM TO BE SOLVED: To provide a method and device for detecting moving object so as to determine correctly existence of a moving object even under the condition where a background changes at very close intervals and perform properly updating of the background data. SOLUTION: The device comprises a transmitter 16 which sends a short-time ultrasonic signal intermittently, a receiver 18 which receives a reflected wave received every signal sending, a receiving circuit 20 which gets a received data in time sequence corresponding to its propagated time based on the received reflected wave, and a central calculating device 22. The central calculating device compares the received data delivered from the receiving circuit 20 with a threshold level predetermined according to the propagated time. When the received data is larger than the threshold level straight in a predetermined number of comparisons, the central calculating device determines that a moving object exists. Additionally, it calculates the difference of the this-time received data and the last-time received data from the receiving circuit 20. When the difference is found within acceptable change area straight in another predetermined number of calculations, it updates the threshold level, based on the latest received data.