Scanning a subject with an ultrasonic probe and obtaining an ultrasonic image of the subject. Obtaining a cross-sectional image of a cross-section of a three-dimensional image corresponding to the ultrasonic image from the three-dimensional image, the three-dimensional image including a puncture line set for a puncture needle and a superimposed columnar index having a central axis line on the puncture line and opacity which is reduced with the distance from the central axis line. Displaying the ultrasonic image and the cross-sectional image. In this case, the thickness, opacity, and cross-sectional shape of the index displayed on the cross-sectional image vary according to the positional relationship between the scan plane of the ultrasonic probe and the cross-section in which the puncture line is set.
