PURPOSE: To attain accurately the azimuth of a detected object, which exists in a near position by forming the arrangement of arranged vibrators into the same shape as a spherical wave of the acoustic wave coming from the near position.

CONSTITUTION: A recording circuit 6 reads out stored data of eight channels in accordance with the counted value of a counter 8, and read-out stored data are transmitted as square waves of eight channels from latch circuits 901W908. Square wave train data of eight channels having phase relations related to the azimuth and the distance of a sound source are transmitted from a storage circuit 7 through latch circuits 161W168. Square wave trains of eight channels transmitted from circuits 161W168 are sent to exclusive OR gates 311W318 together with square wave trains of circuits 901W908 with respect to individual channels. Outputs of these gates are led to mixing circuits 201W208 through filters 321W328 and preamplifiers 301W308 to make phases of received signals in ultrasonic oscillators T1WT8 equal to the phase of the spherical wave due to sounds in the near position.