PURPOSE: To obtain resolution in an angular direction and to enable short-time detection by providing a body detecting circuit and a signal processing circuit which sends out a control signal to a delay circuit according to the detection signal from the body detecting circuit.

CONSTITUTION: Transmitting and receiving circuits A1 and A2 send transmitting signals to ultrasonic vibrators S1 and S2 and also amplify signals received from the vibrators S1 and S2. The body, detecting circuit 3 detects the presence of a body at the time of receiving a received pulse in a wave reception section, calculates the distance to the body from the time delay of the received pulse from the transmitting pulse, and sends out a distance signal to a display device 5. The signal processing circuit 4 sends out a signal indicating the delay time corresponding to the set scan angle of a directional beam to the delay circuit 1 according to the body detection signal from the circuit 3. The circuit 1 sets the delay time with this signal, and sends the transmitting signal to the vibrator S2 and the signal of the position of the detected body to the display device 5. Consequently, when the body is detected, the directional beam width is reducible, the scan angle is decreased, and the resolution in the angular direction is detected in a short time.