Gamma rays obtained from radioisotope administered to an examinee are detected by a gamma ray information-detecting unit so that a first tomographic image obtained therefrom is formed on a CRT. Further, a second tomographic image of the examinee detected by using an ultrasonic wave information-detecting unit juxtaposed with respect to the gamma ray information-detecting unit is formed while making the second tomographic image overlap on the first tomographic image. Thus, it is possible to obtain a tomographic image in which relative positional relationship of tissue is clear.