A power source apparatus of a car is provided with contactors (2) connected to an output-side of a battery (1); a pre-charge circuit (3) made up of a series connected pre-charge resistor (6) and a pre-charge relay (7), which is connected with a contactor (2) to supply auxiliary charge to a capacitor (21) connected to a car-side of the battery (1); and a control circuit (4) to control the contactors (2) and the pre-charge relay (7). The pre-charge resistor (6) is connected in parallel with a contactor (2), and the pre-charge relay (7) is connected in series with that contactor (2). The control circuit (4) switches the pre-charge relay (7) ON to pre-charge the car-side capacitor (21), and then switches the contactor (2) ON to connect the battery (1) to the car-side.