In a laser device employing an optical resonator which is constructed of a total reflection mirror and a partial reflection mirror, a total reflection plane having an opening is interposed between the partial reflection mirror and the total reflection mirror, the total reflection plane may be formed of, for example, a dielectric thin film or a metallic totally-reflective thin film produced with a cluster ion beam, and the total reflection plane and the total reflection mirror are arranged so as to establish a resonant state. The total reflection plane is formed on an aperture of the partial reflection mirror. The opening of the total reflection plane may be ring-shaped, or a plurality of openings may be provided. The total reflection plane may be located centrally. In a laser device employing an unstable optical resonator, a beam deriving mirror may be disposed within the optical resonator.