Collimator unit, radiation detecting device, and radiodiagnostic system

A pair of holding plates formed with a plurality of grooves each wider than the thickness of each collimator plate are disposed in parallel so that the respective surfaces formed with the grooves confront each other. Urging members are disposed on the holding members. When the urging members slide in the arranged direction of the grooves along the grooves-formed surfaces of the holding members, the urging members urge individual collimator plates inserted in the grooves toward side walls of the grooves. The collimator plates are inserted into the grooves, then the urging members are slid and held in that slide position to urge individual collimator plates into close contact with side walls of the grooves.