Ultrasound diagnostic apparatus includes an unit 7 for forming time series tomographic images on the basis of a reflection echo signals received by ultrasound probe 2, an unit 8 for obtaining the elasticities of body tissue on the basis of the reflection echo signals and forming elasticity images on times series, an unit 9 for forming a superimposition image on time series by superposing the tomographic image on the elasticity image, an unit 43 for inputting an instruction for controlling superimposition image formation, and an unit 10 for displaying the superimposition image. The ultrasound diagnostic apparatus further includes a freezing control portion (7, 8) for outputting an image, as a frozen image, selected in response to a freezing instruction for freezing the display operation on time series of any of the tomographic image or the elasticity image input into the input unit to the superimposition image forming unit.
