Provided are a radiation detection device, in which the peeling of a sheet material that covers the outer peripheral surface can be suppressed, and a method of manufacturing a radiation detection device. A radiation detection device includes: a front surface member; a rear surface member assembled with the front surface member; a radiation detection panel disposed between the front surface member and the rear surface member and detecting radiation incident from the front surface member side; a sheet material that covers an outer peripheral surface of at least one of the front surface member or the rear surface member; a packing, the sheet material being interposed between the packing and the front surface member or the rear surface member; and a holding portion provided in at least one of the front surface member or the rear surface member and holding the packing in a pressed state.