PURPOSE: To attain high resolution conversion in probing, and also, to attain a real time processing, and moreover, to attain the expansion of a probing range while holding the resolution highly.

CONSTITUTION: A difference to a reception wave is calculated by a difference calculating part 3 by executing a convolutional operation based on the result of operation from impulse response arithmetic parts 10, 11-1n in which the peak value of each pulse is a multiplier by setting a transmission waveform as a pulse train, and the estimated value of an unknown impulse response is a multiplicand, and based on the calculated difference, an estimated impulse response is corrected by correcting parts 10a, 11a-1na of the impulse response arithmetic parts 10, 11-1n, and also, the corrected impulse response is supplied to the impulse response arithmetic part of the next stage.