An optical component casing (25) having a plurality of holes penetrating toward the inside thereof includes a casing body which is constituted of a container (25A), in which a plurality of optical components are housed and arranged therein, and a lid (25B), and a plurality of positioning members (253) for positioning the plurality of optical components at predetermined positions in the casing body. The plurality of positioning members (253) abut on the optical components by being inserted through the plurality of holes to position the optical components at the predetermined positions on an illumination optical axis of light beam irradiated by a light source.