A control device controls a beam vibrating mechanism to vibrate a laser beam in a C-shaped vibration pattern in which a beam spot is moved from a first irradiation position at a front end in a cutting advancing direction to a second irradiation position at a rear side and displaced in an orthogonal direction to the cutting advancing direction, and is moved from the second irradiation position to a third irradiation position at a front end and displaced in the orthogonal direction to the cutting advancing direction, and movement from the first irradiation position to the third irradiation position via the second irradiation position, and movement from the third irradiation position to the first irradiation position via the second irradiation position are repeated. The control device performs control to cut the sheet metal by causing beam spots in the first to third irradiation positions to overlap one another.