A precharge controller includes a main contactor, a capacitor, a precharge contactor, a current sensor, and a control unit. When starting a power supply from a battery to load, the control unit starts precharging by closing the precharge contactor when a detected current is equal to a preset value or lower, determines completion of precharging when the detected current once equal to or exceeded a first threshold value falls to a second threshold value or lower, and closes the main contactor.