A first γ-ray generating in a body, caused by a PET pharmaceutical, and a second γ-ray emitted from a γ-ray source and transmitting through the body are detected with a radiation detector. The emission image information (E image information), E0, E1 and E2, at each of patient motion phases, 0, 1 and 2, which divided a respiration period, are prepared by using information obtained from the detected first γ-ray. The transmission image information (T image information), T0, T1 and T2, at each of patient motion phases, 0, 1 and 2, respectively, are prepared, by using information obtained from the detected second γ-ray. Relative displacements, ([F10], [F20]), are determined by superimposing, on T image information T0, other T image information, T1 and T2. The E image information, E1, E2, are superimposed on the E image information E0, by using this relative displacement.