In a system provided with a plurality of photomultipliers, the sensitivities of the photomultipliers relative to one another are detected by comparing the outputs of the photomultipliers generated under irradiation by light emitted from the same light source. The difference between the detected sensitivities relative to one another and predetermined sensitivities relative to one another is calculated, and the sensitivities of the respective photomultipliers are corrected so that the difference becomes zero.
Method of detecting sensitivities of photomultipliers