PROBLEM TO BE SOLVED: To provide a fat diagnostic device which can be post-fitted to an existing ultrasonic diagnostic apparatus and can perform safe fat diagnosis of the living body deep part such as a liver.SOLUTION: A fat diagnostic device 10 attached to an ultrasonic diagnostic apparatus 1 comprises: a sub probe 4 capable of emitting an ultrasonic wave for heating a fat measurement control part 11 which performs heating control by emitting the ultrasonic wave generated by an ultrasonic wave source 21 for heating to a measurement portion via the sub probe 4, and performs control to measure echo signals before and after heating by transmitting pulse signals via the sub probe 4 a fat information calculation part 12 which calculates fat information including the ultrasonic velocity change from the echo signals before and after heating and a probe holder 5 to which a main probe 2 and the sub probe 4 are mounted, which is provided with a common emission port 5d for emitting the ultrasonic wave emitted from each probe to the measurement portion and makes any one of the ultrasonic waves transmitted/received in a selective manner.
