A body fat diagnostic apparatus, with which a change in the velocity of ultrasonic waves can be measured and fat can be diagnosed while suppressing the effects of a periodical change due to respiration and heartbeats of a subject, is formed of: a process unit for sequentially acquiring ultrasonic wave echo signals for a number of frames so as to form a group of B mode images a data storage unit for storing the ultrasonic wave echo signals corresponding to the groups of B mode images a sampling unit for sampling one frame as a standard image and another frame as a comparative image through the calculation of a cross correlation and a velocity change analyzing unit for forming an image by calculating a change in the velocity of ultrasonic waves on the basis of the ultrasonic wave echo signals corresponding to the standard image and the comparative image.
