A shear wave velocity is accurately measured. Time change data of a displacement of a tissue due to a shear wave generated in a test object is calculated from a reception signal obtained by transmitting an ultrasonic wave to the test object and receiving a reflected wave. The time change data of the displacement is converted into spectrum data indicating a displacement distribution in a frequency space having a spatial frequency and a time frequency as two axes. Spectrum data in a predetermined region is extracted by rotating the spectrum data by a predetermined angle in the frequency space, and filtering the rotated spectrum data. A velocity of the shear wave is calculated based on the extracted spectrum data in the predetermined region.
