To generate a light spot having a different size, preferably a different shape on a projection surface by using two cylindrical optical systems provided with different focal distances along the central axes of cylinders mutually interseced in the area of a beam path.

An image forming light beam 19' is reflected as an image forming light beam 19" from a circular mirror 13' to a mirror wheel 24. The rotating shaft 30 of the wheel 24 is perpendicular to a plane fixed by the image forming light beams 19, 19', 19". A light beam 19''' reflected by the wheel 24 executes V-shaped scanning motion by rotation in the direction of an arrow and generates a desired light spot 23 on a recessed and curved projection surface 14. Two cylindrical mirrors 12', 13' around the rotary shafts 20, 20' are made to properly rotate. Cortsequently, the focal distances of the mirrors 12', 13' are made to be different and thus light spots 23 having different sizes and shapes are obtained.