An optical machining apparatus for irradiating light from a light source onto a source to be machined to form a grooves in the surface. The apparatus uses a mask disposed in the path of light from the light source. The mask includes reflective parts for reflecting the light from the light source. The reflective parts are on a first surface of the mask. The mask also includes a reflection member for returning the light reflected at the reflective parts of the mask toward the mask.
