PROBLEM TO BE SOLVED: To provide an attachment device for fat diagnosis which can be post-fitted to an existing ultrasonic diagnostic apparatus and perform fat diagnosis without requiring major modification.SOLUTION: An attachment device 10 for fat diagnosis attached to an ultrasonic diagnostic apparatus 1 comprises: a sub probe 4 which performs light irradiation a heating control part 41 which performs heating control by light irradiation on a measurement portion via the sub probe 4 an echo signal transmission control part 42 which performs control to acquire and transmit echo signals before and after heating measured by using a main probe 2 and the ultrasonic diagnostic apparatus 1 a fat information calculation part 43 which calculates fat information including ultrasonic velocity change from the transmitted echo signals before and after heating and a probe holder 5 to which the main probe 2 and the sub probe 4 are mounted, and which includes a connection member 5a for emitting the ultrasonic wave and light in an overlapped manner from a common emission port so that the axial direction of the ultrasonic wave emitted from the main probe 2 and the axial direction of the light emitted from the sub probe 4 match each other.
