PURPOSE: To perform underwater prospecting accurately by forming a wave transmission/reception beam at an instructed tilt angle constantly regardless of the oscillation of a hull.

CONSTITUTION: An operation circuit 8 calculates a correction angle θx=sin-1 (-sinθfs.sinθr-cosθfs.sinθp)according to a pitching angle θp which is detected by a pitching meter, a rolling angle θr. which is detected by a rolling meter, and a current prospecting azimuth θfs. For speeding up operation, a table ROM where the correction angle θx which is calculated by the expression is written previously for each input data is created and utilized. A correction circuit 9 synthesizes a correction angle θx from the circuit 8 with an instructed tilt angle θ0 to obtain a tilt angle θ. The tilt angle θ is input to a generator 4 of amount of phase-shifting. thus forming the wave transmission/reception beams at the instructed tilt angle θ0 constantly regardless of the oscillation of a hull.