A synchronous switching apparatus for detecting a source voltage of each phase to close each phase at an electrical phase angle predetermined for each phase, including switching devices 1a-1c provided one for each phase for opening and closing an impedance load, switching devices 2a-2c for closing and opening the switching devices 1a-1c for each phase, measuring transformers 5a-5c for measuring source voltages of the respective phases and phase-to-phase voltages, and phase control devices 42 each for issuing a command for energizing the impedance load at an electrical phase angle in a range predetermined for each phase, when detecting a zero point of a source voltage of each phase or a zero point of each phase-to-phase voltage.