PURPOSE: To adjust an image point position and the incident angle of main light simply and highly accurately by converging parallel light flux obtained from a parallel light flux forming means by a condenser, arranging a parallel plane member for adjusting the angle of main light in the parallel light and arranging an image point position adjusting member in an irradiating optical system.

CONSTITUTION: The irradiating optical system 3 is constituted with a beam expander 4 to be used as the parallel light flux forming means for converting light flux obtained from a light source such as a laser into parallel light flux having a prescribed width, the condenser L3 for converging the parallel light flux and a relay system 5. The beam expander 4 consists of lenses L1, L2 and the relay system 5 consists of lenses L4 and L5. The incident angle of the main light reaching an object surface 2 is changed by rotating a halving glass Lh1 to be the parallel plane member arranged in the light flux around a rotating axis 10 rectangular to the optical axis. Similarly, an image point a3 is shifted by rotating a halving glass Lh2 to be the focus point adjusting member around rotating axis 20.