In a PET device, a first detector includes a plurality of first scintillators and detects gamma rays emitted from positron-emitting radionuclides injected into a subject. A second detector is provided on the outer circumferential side of the first detector, includes a plurality of second scintillators arranged in an arrangement surface density lower than that of the first scintillators, and detects gamma rays that have passed through the first detector. A counted information acquiring unit acquires, as first counted information and second counted information, the detection positions, energy values, and detection time regarding gamma rays detected by the first detector and the second detector. Based on the detection time contained in each of the first counted information and the second counted information, an energy value adder generate corrected counted information by summing the energy values contained in the first counted information and the second counted information.