The EUV light rotating ellipsoidal mirror reflectance measuring device according to the present disclosure may be provided with an EUV light source that outputs EUV light toward a rotating ellipsoidal mirror including a rotating ellipsoidal reflective surface, an optical system that makes the EUV light pass through a first focus position of the rotating ellipsoidal mirror and subsequently be incident on the rotating ellipsoidal reflective surface, and a first optical sensor that is arranged at a second focus position of the rotating ellipsoidal mirror and that detects the EUV light reflected by the rotating ellipsoidal reflective surface after having passing through the first focus position.
展开▼
