A power supply apparatus utilizing a secondary battery, which comprises: a control unit that monitors a performance of said power supply apparatus to control it and monitors a malfunction of said power supply apparatus; a secondary battery that is connected to said control unit and discharges an electric current as charged; a main contact provided in a battery circuit network formed between said secondary battery and a load; and characterized by further comprising: an auxiliary contact that is provided in said battery circuit network so as to be connected in series with said main contact, said auxiliary contact being kept in an open state under a non-operating condition of said power supply apparatus, and a malfunction detection circuit (11 a) that is connected to said battery circuit network that includes said main contact, said malfunction detection circuit (11 a) being connected to an output terminal of the secondary battery on a secondary battery side of the main contact and said auxiliary contact, wherein the malfunction detection circuit (11 a) measures a voltage value of the secondary battery, and causes said auxiliary contact to be kept in an open state based on the measured voltage value and operation information on said main contact from said control unit; wherein: when a halting operation of said power supply apparatus is made, said main contact is first opened and then said auxiliary contact is opened, and when a starting operation of said power supply apparatus is made, said auxiliary contact is first closed and then said main contact is closed. a control unit that monitors a performance of said power supply apparatus to control it and monitors a malfunction of said power supply apparatus; a secondary battery that is connected to said control unit and discharges an electric current as charged; a main contact provided in a battery circuit network formed between said secondary battery and a load; and characterized by further comprising: an auxiliary contact that is provided in said battery circuit network so as to be connected in series with said main contact, said auxiliary contact being kept in an open state under a non-operating condition of said power supply apparatus, and a malfunction detection circuit (11 a) that is connected to said battery circuit network that includes said main contact, said malfunction detection circuit (11 a) being connected to an output terminal of the secondary battery on a secondary battery side of the main contact and said auxiliary contact, wherein the malfunction detection circuit (11 a) measures a voltage value of the secondary battery, and causes said auxiliary contact to be kept in an open state based on the measured voltage value and operation information on said main contact from said control unit; wherein: when a halting operation of said power supply apparatus is made, said main contact is first opened and then said auxiliary contact is opened, and when a starting operation of said power supply apparatus is made, said auxiliary contact is first closed and then said main contact is closed. an auxiliary contact that is provided in said battery circuit network so as to be connected in series with said main contact, said auxiliary contact being kept in an open state under a non-operating condition of said power supply apparatus, and a malfunction detection circuit (11 a) that is connected to said battery circuit network that includes said main contact, said malfunction detection circuit (11 a) being connected to an output terminal of the secondary battery on a secondary battery side of the main contact and said auxiliary contact, wherein the malfunction detection circuit (11 a) measures a voltage value of the secondary battery, and causes said auxiliary contact to be kept in an open state based on the measured voltage value and operation information on said main contact from said control unit; wherein: when a halting operation of said power supply apparatus is made, said main contact is first opened and then said auxiliary contact is opened, and when a starting operation of said power supply apparatus is made, said auxiliary contact is first closed and then said main contact is closed. when a halting operation of said power supply apparatus is made, said main contact is first opened and then said auxiliary contact is opened, and when a starting operation of said power supply apparatus is made, said auxiliary contact is first closed and then said main contact is closed.