The present invention provides a beam homogenizer being equipped with an optical waveguide having a pair of reflection planes provided oppositely, having one end surface into which the laser beam is incident, and having the other end surface from which the laser beam is emitted in the optical system for forming the beam spot. The optical waveguide is a circuit being able to keep radiation light in a certain region and to transmit the radiation light in such a way that the energy flow thereof is guided in parallel with an axis of the channel.