ELECTRIC POWER SUPPLY SYSTEM AND CONTROL METHOD FOR ELECTRIC POWER SUPPLY SYSTEM

An electric power supply system includes: a positive-electrode-side contactor inserted into a positive power line; a negative-electrode-side contactor inserted into a negative power line; a pre-charge circuit; an electric potential difference detector that detects an electric potential difference between both ends of the positive-electrode-side contactor; and a contactor controller that receives an output of the electric potential difference detection circuit, and controls the positive-electrode-side contactor and the negative-electrode-side contactor, in which the contactor controller temporarily turns on the positive-electrode-side contactor in a state where the negative-electrode-ide contactor is turned off when the electric power supply system is started, retains an output of the electric potential difference detection circuit during this on period as a correction value, turns off the positive-electrode-side contactor and turns on the negative-electrode-side-contactor after the retention, and turns on the positive-electrode-side contactor when an output of the electric potential difference detection circuit has reached the correction value.