A power supply system comprising: a power converter comprising: a power conversion module that converts output power from three phases, except for an N-phase, of a three-phase four-wire power supply having an R-phase, an S-phase, a T-phase, and an N-phase; a module control power supply unit that generates, from the output power of the three phases, drive control power for driving the power conversion module; a three phase detection unit that detects an open phase and a reverse phase of each phase based on a phase difference between two of the three phases by using the module control power supply unit as a power supply; a drive control unit that controls driving of the power conversion module by using the drive control power generated by the module control power supply unit as a power source; and an N-phase open phase detection unit that detects an open phase of the N-phase by using the drive control power as a power source; a load connected to the power converter; and a main control power generation unit that generates, from the N-phase and one of the three phases, power for a main control unit that controls the load, wherein the N-phase open phase detection unit detects the open phase of the N-phase based on a voltage of the N-phase. a power converter comprising: a power conversion module that converts output power from three phases, except for an N-phase, of a three-phase four-wire power supply having an R-phase, an S-phase, a T-phase, and an N-phase; a module control power supply unit that generates, from the output power of the three phases, drive control power for driving the power conversion module; a three phase detection unit that detects an open phase and a reverse phase of each phase based on a phase difference between two of the three phases by using the module control power supply unit as a power supply; a drive control unit that controls driving of the power conversion module by using the drive control power generated by the module control power supply unit as a power source; and an N-phase open phase detection unit that detects an open phase of the N-phase by using the drive control power as a power source; a power conversion module that converts output power from three phases, except for an N-phase, of a three-phase four-wire power supply having an R-phase, an S-phase, a T-phase, and an N-phase; a module control power supply unit that generates, from the output power of the three phases, drive control power for driving the power conversion module; a three phase detection unit that detects an open phase and a reverse phase of each phase based on a phase difference between two of the three phases by using the module control power supply unit as a power supply; a drive control unit that controls driving of the power conversion module by using the drive control power generated by the module control power supply unit as a power source; and an N-phase open phase detection unit that detects an open phase of the N-phase by using the drive control power as a power source; a load connected to the power converter; and a main control power generation unit that generates, from the N-phase and one of the three phases, power for a main control unit that controls the load, wherein the N-phase open phase detection unit detects the open phase of the N-phase based on a voltage of the N-phase.