A laser apparatus comprising: an optical device having two reflection mirrors (120, 140) arranged to face each other and a single waveguide formed between the two reflection mirrors (120, 140); and a laser irradiation device configured to irradiate the optical device with laser, wherein the optical device is configured so that at least a portion of the laser travels Z in the waveguide by being reflected by the two reflection mirrors (120, 140) in order, wherein the optical device comprises an output surface configured to emit a portion of the laser, the output surface formed on a surface of the first reflection mirror of the two reflection mirrors, wherein the first reflection mirror transmits a portion of the laser and reflects another portion thereof such that the laser portion reflected by the first reflection mirror continues to travel in the waveguide, and the laser portion transmitted by the first reflection mirror is emitted as an output laser from the output surface formed on said surface of the first reflection mirror, wherein the laser irradiation device comprises a plurality of irradiation parts including a first irradiation part configured to irradiate a first laser and a second irradiation part configured to irradiate a second laser, wherein, when viewed from a normal direction of the output surface, either an irradiation direction in which the first irradiation part irradiates the first laser to the waveguide of the optical device is not parallel to an irradiation direction in which the second irradiation part irradiates the second laser to the waveguide of the optical device, or respective incident angles at an input surface of the optical device of the first and second lasers are different, and wherein a traveling direction of the first laser is not parallel to a traveling direction of the second laser in the waveguide when viewed from the normal direction of the output surface, and an emission direction of the first laser from the output surface is not parallel to an emission direction of the second laser from the output surface when viewed from the normal direction of the output surface. an optical device having two reflection mirrors (120, 140) arranged to face each other and a single waveguide formed between the two reflection mirrors (120, 140); and a laser irradiation device configured to irradiate the optical device with laser, wherein the optical device is configured so that at least a portion of the laser travels Z in the waveguide by being reflected by the two reflection mirrors (120, 140) in order, wherein the optical device comprises an output surface configured to emit a portion of the laser, the output surface formed on a surface of the first reflection mirror of the two reflection mirrors, wherein the first reflection mirror transmits a portion of the laser and reflects another portion thereof such that the laser portion reflected by the first reflection mirror continues to travel in the waveguide, and the laser portion transmitted by the first reflection mirror is emitted as an output laser from the output surface formed on said surface of the first reflection mirror, wherein the laser irradiation device comprises a plurality of irradiation parts including a first irradiation part configured to irradiate a first laser and a second irradiation part configured to irradiate a second laser, wherein, when viewed from a normal direction of the output surface, either an irradiation direction in which the first irradiation part irradiates the first laser to the waveguide of the optical device is not parallel to an irradiation direction in which the second irradiation part irradiates the second laser to the waveguide of the optical device, or respective incident angles at an input surface of the optical device of the first and second lasers are different, and wherein a traveling direction of the first laser is not parallel to a traveling direction of the second laser in the waveguide when viewed from the normal direction of the output surface, and an emission direction of the first laser from the output surface is not parallel to an emission direction of the second laser from the output surface when viewed from the normal direction of the output surface.