A power supply apparatus includes: a plurality of batteries; a changeover portion switching the connection between the plurality of batteries; a short-circuit battery detection portion, if an internal short-circuit is produced in any of the plurality of batteries, detecting this internal short-circuit battery; and a changeover control portion, if the short-circuit battery detection portion detects the internal short-circuit battery, allowing the changeover portion to switch the connection between the plurality of batteries in such a way that this internal short-circuit battery and at least one of the other batteries are connected in series to thereby form a closed circuit.