A first sensor panel, a second sensor panel, and a base are accommodated in a housing of an electronic cassette. Circuit substrates are mounted on a rear surface of the base. The base is made of a pitch-based carbon fiber reinforced resin obtained by impregnating a pitch-based carbon fiber with a matrix resin. The fiber directions of the pitch-based carbon fibers are aligned with one direction. Therefore, the base has high thermal conductivity in a direction parallel to the fiber direction. As a result, the driving heat of the circuit substrates is rapidly diffused to the entire rear surface.