A processing circuit, which carries out coincidence counting, acquires calibration data so that time delays of γ-ray detection signals from radiation detectors coincide with one another. A technique for acquiring calibration data faster and easily is provided to attain high time precision and respond to multi-channeling of detectors. A signal from a test signal generator is sent to signal processing apparatuses and coincidence count events are generated as a test. The events generated are processed by a delay time control apparatus and a variable delay circuit is controlled to improve the accuracy of coincidence counting.