A power supply apparatus comprising: a first connection portion configured to be connected to a first DC power supply; a second connection portion configured to be connected to a second DC power supply; a first switching element and a second switching element sequentially connected in series between the first connection portion and ground; an inductor and a capacitor sequentially connected in series between a connection point between the first switching element and the second switching element and the ground; a control unit configured to turn ON/OFF the first switching element (Ql); a voltage detection unit configured to detect a voltage between a connection point between the inductor and the capacitor and the second connection portion; a current direction detection unit configured to detect a direction of a current flowing through the inductor if the voltage detected by the voltage detection unit is equal to or lower than a predetermined value; and a determination unit configured to determine that a low voltage abnormality has occurred, if the voltage detected by the voltage detection unit is equal to or lower than the predetermined value, wherein if the direction of the current detected by the current direction detection unit is a direction from the first connection portion side toward the second connection portion, the determination unit determines that the second connection portion side is abnormal, and if the direction of the current detected by the current direction detection unit is a direction from the second connection portion side toward the first connection portion, the determination unit determines that the second switching element is abnormal. a first connection portion configured to be connected to a first DC power supply; a second connection portion configured to be connected to a second DC power supply; a first switching element and a second switching element sequentially connected in series between the first connection portion and ground; an inductor and a capacitor sequentially connected in series between a connection point between the first switching element and the second switching element and the ground; a control unit configured to turn ON/OFF the first switching element (Ql); a voltage detection unit configured to detect a voltage between a connection point between the inductor and the capacitor and the second connection portion; a current direction detection unit configured to detect a direction of a current flowing through the inductor if the voltage detected by the voltage detection unit is equal to or lower than a predetermined value; and a determination unit configured to determine that a low voltage abnormality has occurred, if the voltage detected by the voltage detection unit is equal to or lower than the predetermined value, wherein if the direction of the current detected by the current direction detection unit is a direction from the first connection portion side toward the second connection portion, the determination unit determines that the second connection portion side is abnormal, and if the direction of the current detected by the current direction detection unit is a direction from the second connection portion side toward the first connection portion, the determination unit determines that the second switching element is abnormal.