PURPOSE: To simplify the connecting section of each component and secure the reliability of the seal of each connecting section by housing a laser medium gas cleaning system in a pressure container.

CONSTITUTION: The entire body of a gas cleaning system is housed in a pressure container 1. A laser medium gas 2 pressurized by means of a fan 15 is oscillated by the discharge between main discharge electrodes 19a and 19b when the gas 2 passes between the electrodes 19a and 19b and a laser beam is emitted from a window 3. When the discharge takes place, fine dust is generated. Part of the gas 2 passed between the electrodes 19a and 19b enters a filter container 18 from a filter entrance 7 or 8 and is discharged to the vicinity of a window 3 from a cleaned gas discharge pipe 4 after the gas 2 is cleaned through a filter 14. The cleaned gas 2 is further discharged to the space between the electrodes 19a and 19b from a laser transmissive port 24. Therefore, the entire body of this laser oscillator can be miniaturized and the seal of the connecting section of each component can be simplified.