In a PET (Positron Emission Tomography)-MRI (Magnetic Resonance Imaging) apparatus of an embodiment, a magnet that is a seamless structure generates a static magnetic field in a bore having a cylindrical shape. First detectors and second detectors are each formed in a ring shape and detect gamma rays emitted from positron emitting radionuclides injected into a subject. The first detectors and the second detectors 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.
