A positron emission computed tomography apparatus according to an embodiment includes a detector, a coincidence counting information generating unit, and a body movement detecting unit. The detector detects annihilation radiation released from a subject. The coincidence counting information generating unit searches for sets of counting information, which counted a pair of annihilation radiations at substantially the same time, from a counting information list that is generated from output signals of the detector； generates a set of coincidence counting information for each retrieved set of counting information； and generates a time series list of coincidence counting information. Based on the time series list of coincidence counting information, the body movement detecting unit detects temporal changes in the body movement of the subject.
