Nuclear medicine diagnosis device and image processing method

A nuclear medicine diagnosis device according to one embodiment of the present invention is provided with the following: a gamma ray projection data acquisition unit for acquiring gamma ray projection data on the basis of gamma rays emitted from a radioisotope administered to a subject; and a scattered radiation correction unit for correcting scattered radiation of the gamma-ray projection data, on the basis of a second x-ray CT image in which the pixel values of a non-subject region which is included in a first x-ray CT image are replaced with specific pixel values.