PURPOSE: To continuously change delay time by an electric signal impressed to a control terminal and to prevent a noise component from being mixed based on the above-mentioned electric signal at the delay circuit in the phasing circuit of the ultrasonic diagnostic device.

CONSTITUTION: Inductors L and L' and variable capacity diodes VC and VC' to change electrostatic capacity according to the size of a backward voltage are used, and a balanced circuit is composed of these inductors and variable capacity diodes. Then, a variable delay line 12 is provided to change the delay time according to the change of the backward voltage at the variable capacity diodes VC and VC'. Then, the delay time is continuously changed according to the change of the backward voltage at the variable capacity diodes VC and VC' due to this variable delay line 12, and the noise component is prevented from being mixed based on the electric signal for control.