An imaging part transmits ultrasonic waves to a specific tissue having a tubular morphology in a three-dimensional region and acquires volume data showing the specific tissue. A tomographic image generator generates tomographic image data in a specified cross-section of the specific tissue based on the volume data. A boundary setting part sets a boundary of the specific tissue shown in the tomographic image data. A developed image generator sets a viewpoint at a specified position with respect to the boundary and executes a rendering process on the volume data along a view direction from the viewpoint toward the boundary, thereby generating developed image data in which the specific tissue is developed along the boundary. A display controller controls a display to display a developed image based on the developed image data.
