The construction of this invention includes an active matrix substrate, an amorphous selenium layer, a high resistance layer, a gold electrode layer, an insulating layer and an auxiliary plate laminated in this order. In one aspect of the present invention, the insulating layer has an inorganic anion exchanger added thereto in order to provide a radiation detector which prevents void formation and pinhole formation in the amorphous semiconductor layer and carrier selective high resistance film, without accumulating electric charges on the auxiliary plate. The inorganic anion exchanger adsorbs chloride ions in the insulating layer, thereby preventing destruction of X-ray detector due to the chloride ions drawn to the gold electrode layer.