PURPOSE: To minimize dross adherence to the inner periphery of a metal workpiece by making coolant flow through one part of the inner surface of the metal workpiece, bringing it into contact with the workpiece and flushing out dross formed during cutting.

CONSTITUTION: Coolant pumped into a laser cutting device 1, passing through in the direction of the arrow A, is made to flow through a rotary table device 20 and a workpiece 5, and is brought into contact with the inner periphery of the workpiece before leaving outward. Cuherent light beam is focused on the surface of the workpiece 5 by a laser 7, the workpiece is heated by the light beam, whereby the residue of molten stainless steel or dross 8 drops into the workpiece. The molten dross 8 is solidified when it comes into contact with the flowing coolant and is flushed out from the end of the workpiece 5 coming into contact with a tail end pressing device 50. The coolant and the dross 8 leave the workpiece 5, drop on a machine table 3, next are collected by a trough or a tank 15, are poured into a coolant tank 10, and the dross is removed by a filter 16 in the coolant tank before recirculating the coolant.