To provide a laser oscillator allowing the use of a plastic lens in a semiconductor laser module for a high-output laser oscillator while being unlikely to reduce the efficiency of coupling to an optical fiber even if a laser output changes. A laser oscillator comprises a semiconductor laser module with multiple semiconductor laser elements. The laser oscillator comprises: multiple lenses in a first group provided in the semiconductor laser module for causing laser beams from the semiconductor laser elements to pass through; and a lens in a second group provided in the semiconductor laser module for causing all beams having passed through the multiple lenses in the first group to pass through. The lenses in the first group are plastic lenses. The lens in the second group is a glass lens.