There is provided an AC power supply for a sputtering apparatus in which the AC power supply can prevent the induction of an arc discharge by suppressing an overvoltage to be generated when the polarity of each electrode is reversed. A bridge circuit made up of a plurality of switching transistors SW1-SW4 is disposed between positive and negative DC current output lines from a DC electric power supply source. An inductor DCL which makes a DC output to have a constant-current characteristic is disposed in at least one of the positive and the negative DC output lines from the DC electric power supply source to the bridge circuit, and a snubber circuit is disposed in parallel with inputs of the bridge circuit.