A laser power supply apparatus supplies AC power to a gas contained in a laser device by way of a pair of dielectric layers, without having to use a transformer to form a high-frequency discharge in a gas to excite the gas, to cause the laser device to radiate. The laser power supply apparatus includes an inverter having arms, each arm including high-speed semiconductor switches connected in series, for directly converting a DC high voltage from a DC power supply to a series of AC output pulses having a much higher AC voltage than the DC high voltage and supplied to the laser device by simultaneously turning on and off those high-speed semiconductor switches in each of the arms, and for furnishing the series of AC output pulses to the laser device at a pair of output terminals.