A display controller causes a display to display a 3-dimensional B-mode image and a 3-dimensional colored Doppler image in a superimposed state. A marker generator generates three planar markers that are orthogonal to each other, and the display controller causes the display to display the three planar markers so as to be superimposed on the 3-dimensional B-mode image and so on. An image generator generates 3-dimensional B-mode image data of a region other than a region existing on a viewpoint side of regions sectioned by the three planar markers. Further, the image generator generates 3-dimensional colored Doppler image data for the region on the viewpoint side. For the region existing on the viewpoint side, only a 3-dimensional colored Doppler image is displayed on the display. An intersection of the three planar markers is set as a sample marker, and Doppler data of the intersection is acquired.