To shorten cycle time in continuously cutting into a constant dimension.

Air nozzles 21 and 21 for jetting compressed air from a feed direction of a workpiece W are provided in the vicinity of an edge of a circular saw blade 9 mounted on a circular saw motor 11. After cutting, retreat motion of the circular saw motor 11 is started after the compressed air is jetted from the air nozzles 21 and 21, and control of stopping the jet of the compressed air takes place when the circular saw motor 11 returns to a waiting position. The air nozzles 21 and 21 are provided at the tip of an air passage incorporated in a saw blade cover covering the circular saw blade. A universal hose 27 for introducing the compressed air from a compressed air source 2 is connected to the air passage 25. A controller 40 outputs an instruction for controlling to open/close an air valve 29 provided at an inlet of the air passage 25.