A temporal change at each coordinate of interest which is spatially fixed in frame data of a plurality of time phases obtained by transmitting and receiving ultrasound is made understandable. A trace processor derives an amount of temporal change at each coordinate of interest of a plurality of coordinates of interest which are spatially fixed in the frame data over a plurality of time phases. The trace processor also derives an amount of spatial movement of each site of interest based on the amount of temporal change of each coordinate of interest near each site of interest. Further, the trace processor derives an amount of spatial movement of each site of interest for each time phase over a plurality of time phases in a trace period, and traces a motion of each site of interest in the trace period based on the amount of movement derived for each time phase.
