A power supply device for an electric discharge machine includes a DC power supply which is connected in parallel to an electrode gap, a plurality of switching elements which are in parallel to each other and which are arranged between the electrode gap and the DC power supply, a current value acquisition unit for acquiring a value of a current, and an ON-OFF control unit which, during the time when the current value reaches a predetermined value until the time when the current starts to fall, sets a cycle for switching the plurality of switching elements from off to on to the same cycle, switches the plurality of switching elements from off to on in a predetermined order for each timing of a phase of 90°, which is 360° divided by the number of the plurality of switching elements, sets an ON-period of each of the plurality of switching elements based on a difference between the value of the current and the predetermined value, and performs ON-OFF control of the plurality of switching elements based on the cycle, the timing, and the ON-period.