1. An ultrasonic diagnostic apparatus comprising: a transmitting/receiving wave unit for sending and receiving ultrasonic waves, and acquiring two-dimensional image data for each transmitted/received wave frame, an extracting unit for extracting an outline of a ventricle or an atrium of a heart based on said two-dimensional image data, a dividing unit for radially dividing an area inside said outline into plural division regions from a reference point set in said ventricle or atrium, an area computing unit for computing an area of each of said division regions for each of said transmitted/received wave frames, and a graph drawing unit for drawing a graph showing a time-dependent variation of the area or an area variation rate of each division region.