An ultrasonic image 105, 106 is captured by an ultrasonic probe 104. A reference image 111 is obtained by extracting a tomographic image corresponding to the scan plane of the ultrasonic image from volume image data that is pre-obtained by a diagnostic imaging apparatus 102 and that is stored in a volume-data storing unit 107. The ultrasonic image and the reference image 111 are displayed on the same screen 114. In this case, of the reference image, a portion corresponding to the view area of the ultrasonic image is extracted and the resulting reference image having the same region as the ultrasonic image is displayed as a fan-shaped image.
