An image sensor assembly is mounted and fixed on a mount substrate with an adhesive, and a light sensitive portion of the image sensor assembly is located so as to reach the vicinity of at least one peripheral region. A moisture-proof protective film to cover a scintillator layer of the image sensor assembly is laid so as to cover the scintillator layer over a side wall to which the light sensitive portion is in proximity, up to the back side of a substrate of the image sensor assembly, and this portion on the back side is sandwiched between the image sensor assembly and the mount substrate so as to be fixed.