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 .