PURPOSE: To obtain precise directivity even if tapped delay wire having low delay time precision is used, by providing memory latch to temporarily store the position to select the tapped delay wire of ordinary delay time precision as a set of delay circuit in each ultrasonic vibrator.

CONSTITUTION: The delay time of input signal entering a delay circuit is controlled by a scanning control circuit. A set of delay circuit consistis of first and second tapped LC delay wires 21a, 21b, first and second selecting switches SW 22a, 22b connected to the output terminals thereof, a memory latch 23 connected to each control terminal, and a buffer amplifier 24. Since the tapped LC delay wires 21a, 21b have a delay time error between each other, the delay time when each SW is turned on is measured beforehand on the tap of each delay wire in the delay circuit, and the combination of switches closest to the delay time required in each angle direction is stored in the address corresponding to each angle in a PROM 26. Reading SW number from this PROM 26 in each direction, the designated SW is turned on.