The radiation detector includes: a sensor board including a flexible substrate and a layer which is provided on a first surface of the substrate and in which a plurality of pixels, which accumulate electrical charges generated in accordance with light converted from radiation, are formed; a conversion layer that is provided on a side, opposite to the substrate, of the layer in which the pixels are formed, and converts radiation into light; protective film that covers at least the conversion layer; a reinforcing member provided on a second surface opposite to the first surface of the substrate; and a supporting member that supports the reinforcing member with the reinforcing member sandwiched between the supporting member and the second surface of the substrate.