PURPOSE: To emit laser beams which do not pulsate from an oscillator so as to enable precise processing by attenuating the pulsation in a pressure reducing room after cooling and decompressing, with a heat exchanger, laser gas which is pulsatively sent from an air blower into a box body.

CONSTITUTION: Laser gas 5 sent from a laser oscillator is sent to a cooler 7B through a pipe 8A, and its output gas is supplied to a volume type air blower 6. The output gas of this air blower 6 is introduced to a cooler 7A. A connection pipe 14 is provided at the lower part outside the box body 11 of this cooler 7A, and the lower part of the pressure reducing room 13 is connected to this pipe 14, and at the upper end of the reducing room 13 a pipe 15 is introduced to the discharge part of the laser oscillator. In this cooler 7A, through the gas 5 which is sent pulsatively from an air blower 6 to the box body is compressed by the air blower 6 and pulsates and is warmed, after it is cooled with a heat exchanger 12 and reduced for pressure, the pulsation attenuates in the pressure reducing room 13, and it is sent to the discharge part of the laser oscillator. Hereby, the laser beam do not pulsate, so precise processing can be done.