A method of manufacturing a radiation detector includes: forming a substrate in which a flexible base material is provided via a peeling layer on a support body and plural pixels that accumulate electric charges generated in response to light converted from radiation are provided in a pixel region of the base material; forming a conversion layer for converting the radiation into light on a surface of the base material; providing a first reinforcing substrate on a surface of the conversion layer opposite to a surface on the substrate side; peeling the substrate provided with the conversion layer and the first reinforcing substrate from the support body; providing a second reinforcing substrate on a surface of the substrate peeled from the support body; and peeling the first reinforcing substrate from the substrate provided with the conversion layer after providing the second reinforcing substrate.