The operability of setting movement of a Doppler sample gate for setting a Doppler measurement portion on a sectoral or circular ultrasonogram is improved. An ultrasonograph is provided with calculation means (25) for determining the position where a Doppler sample gate is displayed after the gate is moved, with reference to the current position where the Doppler sample gate is displayed, according to the amount of movement of the Doppler sample gate position input through a tack ball (23). The calculation means decomposes the amount of movement in orthogonal two-axis direction input through a track ball (23) into a component in the direction of the ultrasonic beam line of an ultrasonogram and a component orthogonal to the former component, determines the ultrasonic beam line after the movement from the decomposed orthogonal components, determines the depth position of the ultrasonic beam line after the movement from the decomposed component in the ultrasonic beam line direction, and changes the display position of the Doppler sample gate to the determined display position after the movement. Thus, the movement of the Doppler sample gate corresponds to the operation of the track ball on the screen irrespective of the position in the sectoral or circular display area, thereby mitigating the feeling of strangeness and improving the operability.
