Provided is a cassette type radiation image detector, which is FPD, having compatibility with a cassette for CR, exhibiting sufficient strength while being thin, capable of limiting deformation of housing against external stress, and capable of performing portable radiography. A cassette type radiation image detector (1) comprises a detector unit (2) having a scintillator (211) for converting radiation into light and a detection section (151) for converting light into an electric signal, and a housing (3) having body section (31) in the shape of square tube formed of plate-shaped carbon fibers (31A) and having openings (311, 312) at the opposite ends thereof, and a first lid member (32) and a second lid member (33) and incorporating the detector unit (2). The body section (31) has the side (X) of incident plane of radiation and the side (Y) of opposite plane, and fiber directions (F, F*) of the plate-shaped carbon fibers (31A) forming respective planes are inclined to openings (311, 312), respectively, and the fiber directions (F, F*) are differentiated from each other.
