On an optical path between a light source and an objective lens, there is provided an optical path changing section for changing a predetermined optical path of undesired light passing through, from the predetermined optical path to another optical path. The optical path changing section includes a plate having an aperture portion for allowing a laser beam emitted from the light source to pass through, and an aperture wall which defines the aperture portion of the plate includes a taper portion which is formed in a tapered-shape and slants so as to come close to an optical axis L1 of the light source in association with movement toward a laser beam outgoing direction. The undesired light from the light source is reflected by the taper portion to change the predetermined optical path of the undesired light passing through, from the predetermined optical path to another optical path.