By the present invention, a thin radiation measuring apparatus equipped with sufficient signal volume is achieved. The radiation measuring apparatus 101 comprises a control device 301, a CCD camera 302, a housing 303, a mirror 304, and a fluorescent body 305. When a beam passes through the fluorescent body 305, fluorescent light is generated at the position where the beam has passed. The strength of the fluorescent light depends on the strength of the beam. The fluorescent light is reflected by the mirror 304 and ultimately observed by the CCD camera 302. The fluorescent body 305 is provided with a reflection preventing film 401 on the mirror-side surface thereof for preventing scattered light from being reflected by the fluorescent body 305 to be incident on the CCD camera 302. If scattered light 402 becomes incident on the reflection preventing film 401, one portion thereof is reflected by the surface of the fluorescent body 305 and another portion is reflected by the surface of the reflection preventing film 401 (reflection light 403A, 403B). The reflection light 403A and the reflection light 403B are in opposite phases and interfere with each other to cause a reduction in amplitude. Thus, the reflection preventing film 401 suppresses reflection of scattered light on the fluorescent body 305 to prevent the scattered light to be incident on the CCD camera 302.Par la présente invention, un appareil de mesure de rayonnement mince équipé de volume de signal suffisant est obtenu. Lappareil de mesure de rayonnement 101 comprend un dispositif de commande 301, une caméra CCD 302, un boîtier 303, un miroir 304 et un corps fluorescent 305. Lorsquun faisceau passe à travers le corps fluorescent 305, une lumière fluorescente est générée au niveau de la position où le faisceau est passé. Lintensité de la lumière fluorescente dépend de lintensité du faisceau. La lumière fluorescente est réfléchie par le miroir 304 et, enfin, observée par la caméra CCD 302. Le corps fluorescent
