A configuration of detecting light from the front face of a light source is the best for confirming the variation of a light quantity, but when a plurality of light sources are present, as many detectors for checking a light quantity as the light sources are necessary and the apparatus configuration becomes complex. In the present invention, a detector for checking a light source light quantity is installed in a reaction container transfer mechanism used commonly for a plurality of detection sections, and the light quantities of light sources are checked with the detector.