A radiation detector includes a sensor substrate, a conversion layer, and a reinforcing substrate. In the sensor substrate, a plurality of pixels for accumulating electric charges generated in response to light converted from radiation are formed on a pixel region of a flexible base material. The conversion layer is provided on a first surface of the base material on which the pixels are provided and converts radiation into light. The reinforcing substrate is provided on a surface of the conversion layer opposite to a surface on the base material side and includes a porous layer having a plurality of through-holes to reinforce the stiffness of the base material.