PURPOSE: To reproduce a Doppler signal with good sound quality by multiplying a spectrum inputted from a Fourier transforming part with a prescribed high- pass filter to be stored beforehand, removing the clutter of a reduction and inverse transforming only a Fourier arithmetic output at a threshold or above.

CONSTITUTION: An ultrasonic wave is transmitted and received from an ultrasonic wave probe 1 to a subject to be checked, a Doppler deviation signal is detected from the signal obtained by it through filters 6a and 6b, the signal is digital-converted by A/D converters 7a and 7b, the signal is Fourier- transformed by a Fourier transforming part 8, it is written to an image memory 10, simultaneously, a TV scanning conversion is executed, and blood flow velocity information is displayed. By a processing means 30, the spectrum inputted from the Fourier transforming part 8 is multiplied with the prescribed high-pass filter stored beforehand, the clutter is filtering-processed, only the output at the prescribed threshold or above is obtained, and simultaneously, data are replaced on the above-mentioned spectrum. The Fourier inverse transforming is executed by a converting means 31, and an audio signal is outputted as a Doppler sound by a voice means 20.