HUMAN BODY DETECTING DEVICE

PURPOSE:To improve detection precision without requiring sensitivity adjustment by setting the reference time between the transmission and reception of ultrasonic waves when a reset switch is turned on, and comparing the measured time with the reference time after the reset switch is released. CONSTITUTION:When a power source is turned on, a reset switch 2 is turned on into the reset state to set and store the reference time according to the environment, a transmission signal is outputted from an oscillating circuit 4 by the command from a micro-computer 3A, and ultrasonic waves from a transmitting sensor Q1 are transmitted to a human body detection region. When the ultrasonic waves are reflected from a background object B and received by a receiving sensor Q2, the reception signal is amplified by an AMP 5 and detected by a detecting circuit 7 via a filter circuit 6, and the time from transmission to reception is counted by the micro-computer 3A. When the count number is equal to the count number of the reference time specified times or above, the reset switch 2 is turned off, and the human body detection state is set. When the measured count number is smaller than the reference time, it is judged that a human body exists, and the human body detection process is performed.