The reduction sensitization centers on AgBr emulsion grains have their own molecular absorption band centered at 455 nm, as measured by the diffuse transmittance spectroscopy method for coated emulsion layers. The spectral sensitization caused by this molecular absorption has been examined quantitatively. It is concluded that the reduction sensitization centers spectrally sensitize the AgBr grains with a markedly high quantum efficiency, but with an action spectrum substantially different from the absorption spectrum. The electron transfer from the excited state of the reduction sensitization center, reasonably accounting for the experimental observations, is discussed.