A contour specifying part receives volume data representing a subject acquired by transmission of ultrasonic waves to the subject, and specifies a 3-dimensional contour of a myocardium based on the volume data. A forming part sets a reference point on the contour of the myocardium, and forms an image generation plane including a plane substantially orthogonal to the contour of the myocardium at the reference point. An image generator generates image data on the image generation plane based on the volume data. A display controller controls a display to display an image based on the image data.