A cassette type radiation image detector having a box-shaped cassette housing configured by engaging a front member that is light-shielding and radiation-transmissive, with a light-shielding back member, and a two-dimensional array type radiation detection sensor for detecting radiation images incorporated in the radiation image detector, the radiation image detector including: a sensor supporting member that supports the radiation detection sensor; a first engaging member provided at the sensor supporting member; a second engaging member provided at the back member; and a shock absorbing member positioned between the first engaging member and the second engaging member, wherein the box-shaped cassette housing is formed by engaging the first engaging member with the second engaging member via the shock absorbing member.