The radiation detector includes a sensor substrate and a reinforcing substrate. In the sensor substrate, a plurality of pixels for accumulating the charges generated according to light converted from radiation are formed in the pixel region on the first surface of the flexible base material, and the terminal for electrically connecting a flexible cable to the first surface is provided. The reinforcing substrate is provided on the second surface opposite to the first surface of the base material in a region excluding at least the facing region facing the terminal to reinforce the stiffness of the base material.