A power supply apparatus includes: a plurality of power supply units; a positive polarity coupling portion; and a negative polarity coupling portion; each of the power supply units is provided with: battery units; first relays connected in series to the battery units, capable of disconnecting electrical connection between the battery units and any one of the positive polarity coupling portion and the negative polarity coupling portion; resistor elements having one ends which are connected to the battery units between the battery units and the first relay; a resistor coupling portion; and a second relay connected to the resistor coupling portion, capable of disconnecting electrical connection between the resistor coupling portion and any one of the positive polarity coupling portion and the negative polarity coupling portion which is connected to the first relays, the second relay having fewer in number than the number of the power supply units.