Three-dimensional image data is constructed without reducing precision of tomographic image data by each radial scanning which is acquired by scanning in a longitudinal axis direction of a probe even when a variation of rotational speed of radial scanning occurs due to a variation of torque in wave radiation from a probe distal end. A signal processing unit is configured by including an A/D conversion section, a line data generating section, a frame memory section, a memory control section, a data recording control section, an image constructing section, a data recording section, an longitudinal moving amount calculating section and a control section. The frame memory section stores reflection intensity data from the line data generating section by frame unit based on a rotation detection signal Sa, and is configured by including a first memory, a second memory and a third memory which are constituted of three frame memories for storing reflection intensity data of three frames.
