In an ultrasonic diagnostic apparatus (1000), ultrasonic propagation time differences contained in echo signals reflected from a biological body under medical examination are corrected by comprising: a quadrature phase detecting unit (30:130:25) for quadrature-phase-detecting the echo signals derived from an ultrasonic transducer probe (2) to obtain as phase data a quadrature signal component and an in-phase signal component; a delay-time correcting value calculating unit (23) for calculating at least one of delay-time correcting values used for the energizing signals and the echo signals based upon both of the quadrature signal component and in-phase signal component: and, a delay controlling unit (13) for controlling at least one of delay time data previously given to the energizing signals and echo signals based upon one of calculated delay-time correcting values.