For the purpose of mixing laser light (P0) from a laser light source (18), the laser light (P0) is made incident on a first end surface of an optical fiber (24), and is emitted from a second end surface of the optical fiber (24). Subsequently, laser light (P1) emitted from the second end surface of the optical fiber (24) is made incident on a first end surface of an optical fiber (28), and is emitted from a second end surface of the optical fiber (28). A swinging micro-electromechanical system (27) having a mirror plate (27a) is interposed between the second end surface of the optical fiber (24) and the first end surface of the optical fiber (28). Thus, the mirror plate (27a) is swung, and a laser beam (P4) is thereby shifted and mixed.