A system comprising a gas laser oscillator having a discharge part in which an electrostatic capacity discontinuously changes and a power device configured to supply an electric power to the gas laser oscillator, the power device comprising: a converter part configured to convert an AC voltage to a DC voltage, an inverter part that has a switching element and a circulating current diode connected in parallel with the switching element and being configured to convert the DC voltage outputted from the converter part to an AC voltage, a transformer that has a first inductance forming a series resonance circuit with an electrostatic capacity of the gas laser oscillator and being configured to convert the AC voltage outputted from the inverter part; and a second inductance connected to an output part of the inverter part in parallel with the transformer; wherein the value of the second inductance is set so that when the switching element is turned on to apply a backward voltage to the circulating current diode, and a direction of a current supplied to the transformer is the same as a forward direction of the circulating current diode, an absolute value of the current supplied to the second inductance is to be larger than an absolute value of the current supplied to the transformer; the power device further comprising: a switching unit provided between one end of the second inductance and the output part of the inverter part to switch disconnection and connection of the second inductance to the output part of the inverter part, and a controller configured to control the switching unit to disconnect the second inductance from the output part of the inverter part when a discharge is generated in a discharge part provided in the gas laser oscillator, and configured to control the switching unit to connect the second inductance to the output part of the inverter part when the discharge is not generated. a converter part configured to convert an AC voltage to a DC voltage, an inverter part that has a switching element and a circulating current diode connected in parallel with the switching element and being configured to convert the DC voltage outputted from the converter part to an AC voltage, a transformer that has a first inductance forming a series resonance circuit with an electrostatic capacity of the gas laser oscillator and being configured to convert the AC voltage outputted from the inverter part; and a second inductance connected to an output part of the inverter part in parallel with the transformer; wherein the value of the second inductance is set so that when the switching element is turned on to apply a backward voltage to the circulating current diode, and a direction of a current supplied to the transformer is the same as a forward direction of the circulating current diode, an absolute value of the current supplied to the second inductance is to be larger than an absolute value of the current supplied to the transformer; a switching unit provided between one end of the second inductance and the output part of the inverter part to switch disconnection and connection of the second inductance to the output part of the inverter part, and a controller configured to control the switching unit to disconnect the second inductance from the output part of the inverter part when a discharge is generated in a discharge part provided in the gas laser oscillator, and configured to control the switching unit to connect the second inductance to the output part of the inverter part when the discharge is not generated.