According to one embodiment, a power supply circuit includes at least an input phase determining unit and an input phase switching unit. The input phase determining unit is configured to determine, of three phases of the input three-phase alternating current, a phase of a highest voltage and a phase of a lowest voltage at a given time. The input phase switching unit is configured to switch an input voltage to a primary coil of a transformer so as to input, during a first switching period, a voltage of the highest voltage phase to one terminal of the primary coil and a voltage of the lowest voltage phase to another terminal, and configured to input, during a second switching period being contiguous to the first switching period, a voltage of the lowest voltage phase to the one terminal and a voltage of the highest voltage phase to the another terminal.
