In a PET (Positron Emission Tomography)-MRI (Magnetic Resonance Imaging) apparatus (100) of an embodiment, a magnet (1) that is a seamless structure generates a static magnetic field in a bore having a cylindrical shape. First detectors (13a, 33a) and second detectors (13b, 33b) are each formed in a ring shape and detect gamma rays emitted from positron emitting radionuclides injected into a subject. The first detectors (13a, 33a) and the second detectors (13b, 33b) are disposed with a space therebetween in an axial direction of the bore so as to interpose the magnetic field center of the static magnetic field therebetween.
