A transmission wave corresponding to an FM continuous wave having been subjected to an FM modulation processing is transmitted from a transmitting transducer 10. A preamplifier 16 generates a reception RF signal and outputs the reception RF signal to a receiving mixer 30. The receiving mixer 30 applies orthogonal detection to the reception RF signal to generate a complex signal. A reference signal supplied to each mixer in the receiving mixer 30 is generated based on an FM continuous wave output from an FM modulator 20. The FM continuous wave output from the FM modulator 20 is delayed by a delay circuit 25, and one signal is directly supplied to a mixer 32 whereas the other signal is supplied to a mixer 34 via a n/2 shift circuit 26. The delay circuit 25 applies a delay processing in accordance with a depth of a target position within a living organism to the FM continuous wave. As a result, Doppler information from the target position can be selectively extracted by a Doppler information analyzing section 44.
