PURPOSE: To utilize auxiliary gas effectively and improve working efficiency by making the position of nozzle of the device freely changeable according to the direction of working and object of working.

CONSTITUTION: When a work 12 moves in the direction of the arrow, a partition plate 15 having a long hole installed under a gas chamber 13 rotates around the axis of the chamber 13, and auxiliary gas from a perforated nozzle acts effectively. Holes arranged in the circumference of the nozzle 16 acts to blow off the heated molten work, and their size and shape can be selected to enhance gas jet effect. The center hole of the nozzle 16 as an exist of a beam spot can be made smaller, and improvement of sectional area properties and reduction of cut width can be expected.