Abstract: An ultrasonic Doppler diagnostic apparatus which transmits an ultrasonic wave into a subject under observation, detects the velocity of movement of a moving reflective member such as blood flow within the heart or a coronary artery of the subject, and displays the detected velocity information as an image. The apparatus transmits an ultrasonic pulsed wave into a subject, receives the echo reflected from the subject, converts the clutter signal contained in the received signal into a complex clutter signal in a complex signal converter, and uses this complex clutter signal as a complex reference signal for mixing with the received signal to produce a complex signal.When the complex clutter signal is used as a complex reference signal in this way, it is possible to obtain a complex signal free of the velocity information related to slow moving members such as the blood vessel wall and the heart wall which is contained in the received signal.