A phase sequence switching device for a three-phase power supply, which is provided in a power supply path from a three-phase power supply to a load, characterized by: a power-supply side relay (7, 11) including two Form C contact relays (7a, 7b, 11b, 11c) connected to two phases of the three-phase power supply respectively, the Form C contact relays (7a, 7b, 11b, 11c) having first travelling contacts (c of 7a, c of 7b, c of 11b, c of 11c) respectively; a load side relay (8, 12) including two Form C contact relays (8a, 8b, 12b, 12c) connected to two phases between the power-supply side relay (7, 11) and the load, the Form C contact relays (8a, 8b, 12b, 12c) having second traveling contacts (c of 8a, c of 8b, c of 12b, c of 12c) respectively; and a switching circuit (9, 13) which switches from a disconnected state to a state where the first traveling contacts (c of 7a, c of 7b, c of 11b, c of 11c) connected to the respective two phases of the three-phase power supply are connected to the respective second traveling contacts (c of 8a, c of 8b, c of 12b, c of 12c) connected to the respective two phases of the load in a positive phase when a relay action of one of the power-supply side relay (7, 11) and the load side relay (8, 12) is performed, the switching circuit (9, 13) switching from the disconnected state to a state where the first travelling contacts (c of 7a, c of 7b, c of 11b, c of 11c) connected to the respective two phases of the three-phase power supply are connected to the respective second traveling contacts (c of 8b, c of 8a, c of 12c, c of 12b) connected to the respective two phases of the load in a reverse phase when a relay action of the other relay (8, 12 or 7, 11) is performed. a power-supply side relay (7, 11) including two Form C contact relays (7a, 7b, 11b, 11c) connected to two phases of the three-phase power supply respectively, the Form C contact relays (7a, 7b, 11b, 11c) having first travelling contacts (c of 7a, c of 7b, c of 11b, c of 11c) respectively; a load side relay (8, 12) including two Form C contact relays (8a, 8b, 12b, 12c) connected to two phases between the power-supply side relay (7, 11) and the load, the Form C contact relays (8a, 8b, 12b, 12c) having second traveling contacts (c of 8a, c of 8b, c of 12b, c of 12c) respectively; and a switching circuit (9, 13) which switches from a disconnected state to a state where the first traveling contacts (c of 7a, c of 7b, c of 11b, c of 11c) connected to the respective two phases of the three-phase power supply are connected to the respective second traveling contacts (c of 8a, c of 8b, c of 12b, c of 12c) connected to the respective two phases of the load in a positive phase when a relay action of one of the power-supply side relay (7, 11) and the load side relay (8, 12) is performed, the switching circuit (9, 13) switching from the disconnected state to a state where the first travelling contacts (c of 7a, c of 7b, c of 11b, c of 11c) connected to the respective two phases of the three-phase power supply are connected to the respective second traveling contacts (c of 8b, c of 8a, c of 12c, c of 12b) connected to the respective two phases of the load in a reverse phase when a relay action of the other relay (8, 12 or 7, 11) is performed.