PROBLEM TO BE SOLVED: To miniaturize and reduce the weight of a radiation generating apparatus including a radiation generating unit 2 which emits radiation, and a movable diaphragm unit 3 which has an envelope 17, a reflecting plate 19 which reflects visible light thereon and transmits the radiation therethrough, restriction blades 18 which adjust a size of a radiation field by adjusting a size of an opening part 21 for passing the radiation from the radiation generating unit 2, and a light source 20 of the visible light which simulatively shows the radiation field in a form of a visible light field by the visible light reflected on the reflecting plate 19.SOLUTION: A reflecting plate 19 is provided orthogonal to a central line Z formed by connecting a focal point X of radiation and a center Y of an opening part 21 of restriction blades 18, and across an irradiation path of the radiation which irradiates the radiation field. A light source 20 can be moved between a first position at which the light source 20 can simulatively show the radiation field by the visible light field, and a second position which is displaced from the irradiation path of the radiation which irradiates the radiation field.【課題】放射線を放出する放射線発生ユニット２と、可動絞りユニット３とを備え、可動絞りユニット３が、外囲器１７と、可視光を反射して放射線を透過させる反射板１９と、放射線発生ユニット２からの放射線を通過させる開口部２１の大きさを調整することで放射線照射野の大きさを調整可能な制限羽根１８と、反射板１９に反射させた可視光による可視光照射野として放射線照射野を模擬表示する可視光の光源２０とを有する放射線発生装置について、小型軽量化を図れるようにする。【解決手段】反射板１９を、放射線の焦点Ｘと制限羽根１８の開口部２１の中心Ｙを結ぶ中心線Ｚに直交し、しかも放射線照射野に照射される放射線の照射経路を横断して設け、光源２０を、放射線照射野を可視光照射野で模擬表示可能な第一の位置と、放射線照射野に照射される放射線の照射経路から外れた第二の位置との間を移動可能とする。【選択図】図１
