A positron emission tomography (PET)-magnetic resonance imaging (MRI) apparatus (100) according to an embodiment includes a gantry having a static magnetic field magnet (1), a gradient coil (3), and a radio frequency coil (5), a PET detector (13, 13a, 13b, 13c), and a moving mechanism (20, 20a, 20b, 20c). The static magnetic field magnet (1) generates a static magnetic field in a bore having an approximately cylindrical shape. The gradient coil (3) is disposed on an inner circumference side of the static magnetic field magnet (1) and applies a gradient magnetic field to an object disposed in the bore. The radio frequency coil (5) is disposed on an inner circumference side of the gradient coil (3) and applies a radio frequency magnetic field to the object. The PET detector (13, 13a, 13b, 13c) detects gamma rays emitted from a positron-emitting radionuclide injected into the object. The moving mechanism (20, 20a, 20b, 20c) causes the PET detector (13, 13a, 13b, 13c) in the gantry along the axial direction of the bore.
