An ultrasound diagnostic apparatus 1 comprises an ultrasonic probe 2 for transmitting the ultrasound while three-dimensionally scanning, and receiving ultrasound reflected from biological tissue, an image processor 5 (and a signal processor 4) for generating image data for an MPR image based on results received thereof, an information memory 6 for storing cross-sectional-position information D showing a cross-section of this MPR image, a display part 81, and a controller 9. The image processor 5 generates image data for the new MPR image for the relevant cross-sectional position, based on the cross-sectional position shown in the cross-sectional-position information D1 obtained when the MPR image was obtained in the past and the received results obtained by the new three-dimensional scan performed with the ultrasonic probe 2. The controller 9 causes the display part 81 to display the new MPR image.