Sensitivity correction for multiple γ radiation detectors is performed by use of sensitivity coefficients obtained through a first sensitivity coefficient calculation step for obtaining sensitivity coefficients, classified according to sensitivity factors, on the basis of coincidence counting data collected as a result of detection of γ radiation emitted from a rotated rod-shaped calibration radiation source, and through a third sensitivity coefficient calculation step for obtaining sensitivity coefficients derived from a geometrical arrangement on the basis of coincidence counting data collected in a state where arrangement of the γ radiation detectors is changed. A re-constructed image is obtained on the basis of data acquired after the sensitivity correction is finished.