Startup method for gas laser unit and gas laser unit having startup function

A discharge excitation gas laser unit capable of generating a laser by circulating a laser gas in a laser discharge tube and generating high-frequency discharge of the laser gas, the gas laser unit comprising:

• a storing part for previously storing an output current characteristic, as a normal current characteristic, of a DC power supply part of a laser power supply unit of the gas laser unit when the gas laser unit is normally activated;
• a detecting part for detecting an output current of the DC power supply part of the laser power supply unit while the gas laser unit is activated;
• and
• a pressure controlling part for controlling the pressure of the laser gas within the laser discharge tube such that the output current of the DC power supply part detected by the detecting part does not exceed a threshold which is determined based on the normal current characteristic stored in the storing part.