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

A startup method capable of easily and inexpensively activating a laser oscillator by limiting an output current of a high-frequency power supply, without using a particular element or a complicated system, even when the laser oscillator is activated in a low-temperature environment, and a gas laser unit having such a function. According to the normal pressure control, the laser gas is gradually increased from pressure p1 to pressure p2. However, in the invention, when DC current reaches a certain threshold at time t3, a feedback control of the laser gas is executed after time t3 such that the DC current does not exceed the threshold. In this case, the laser gas pressure is controlled so as to increase to pressure p2' which is smaller than pressure p2.