PURPOSE: To decrease uneven exposure by irradiating a vertical center, the entire upper part and a lower port of a mirror in the entire exposure range with first, second and third skew incident flat mirrors separately to obtain a large irradiation power.

CONSTITUTION: An SOR light 29 is radiated at a wide diffusion angle horizontally and at a narrow diffusion angle vertically from a light emitting point P on a storage ring. Skew incident flat mirrors 34-36 are arranged in the course of a light drawing line 26 to which the SOR light 29 is introduced. Vertical center of the entire exposure area on a wafer 33 as performed with skew incident flat mirrors 34-36 is exposed with the skew incident flat mirror 34, the upper part thereof with the skew incident flat mirror 35 and the lower part thereof with the skew incident flat mirror 36. Moreover, the flat mirror 34 is oscillated centered on a shaft 38, the flat mirror 35 centered on shafts 39 and 41 and the flat mirror 36 centered on shafts 40 and 42.