PURPOSE: To remove noises from a beam output by dividing the main axis direction of a beam outputted from an adaptive beam former (ABF) into thinner dividing width parts and selecting the 2nd direction discrete value which is the nearest value to a direction to be estimated by an objective direction estimating means.

CONSTITUTION: A discrete value converter 70 selects the nearest value to an output of an objective direction tracker 30 out of the set of the 2nd direction discrete values discreted with the dividing width smaller than that of the set of the 1st direction discrete values of the main axis direction of a beam formed by an unadaptable waiting beam former (CBF)20 and outputs the selected value to a factor calculator 43 and the 2nd delay compensator 80K. The compensator 80K compensates the time delay of an output signal obtained from a detecting element 11K and inputs its output signal to a variable factor filter 41K. After the setting of a delay compensating value in the compensator 80K, the calculator 43 calculates the factor of the filter 41K reversibly. The 2nd dividing width is selected so that the deterioration of the noise removing characteristic of a signal S' outputted from the ABF40 is reduced.