Abstract: A reflection type optical device comprises a convex integration mirror and a concave mirror. The convex integration mirror prepared by arranging side by side a plurality of plane segment mirrors, each preferably having a rectangular or square shape, on a material having convex outer surface so that a laser beam is divided and reflected by the integration mirror as reflected laser beams which are then condensed on a plurality of focal points lying on one plane, preferably at which a metal plate having a plurality of pin-holes substantially corresponding to the numbers of the focal points is located on the plane so that the focal points coincide with locations of the pin-holes, respectively.