A power supply device includes: a first switching element and a flywheel semiconductor element which are connected in series to a first DC power source in this order; and a reactor and a second DC power source which are connected in series in this order to a node between the first switching element and the flywheel semiconductor element. A second switching element and a charge circuit for charging a line between the first switching element and the second switching element are interposed between the reactor and the second DC power source. Abnormality of each element is determined from a voltage of each portion of the power supply device measured when the first and second switching elements and the flywheel semiconductor element are driven and controlled.