Generation of dark current due to emission of back lighting to radiation image detectors is sufficiently suppressed. A radiation image detecting apparatus includes a radiation image detector and a light emitting section. A biasing electrode to which a biasing voltage is applied, a photoconductive layer for generating electric charges when irradiated with recording electromagnetic waves bearing a radiation image, a substrate side charge transport layer for transporting the electric charges which are generated in the photoconductive layer, and an active matrix substrate provided with a plurality of charge collecting electrodes for collecting the electric charges which are generated in the photoconductive layer, are laminated in this order to form the radiation image detector. The light emitting section emits light onto the radiation image detector at least during irradiation of the recording electromagnetic waves. The average composition of the substrate side charge transport layer is SbxS100-x (41≦x≦60).