Provided is a power supply device which uses a simplified device configuration to reliably detect anomalies such as fused contacts, and which eliminates overcharging and secondary battery hazards caused by overcharging. The power supply device (1) is provided with: a control unit (7) for monitoring and controlling the operation of the power supply device (1), and for monitoring anomalies in the power supply device (1); a secondary battery (3) connected to the control unit (7), and for discharging electricity which has been charged; a main contact (9) connected to a battery circuit network (8) formed between the secondary battery (3) and a load (13); an auxiliary contact (10) connected in series to the main contact (9), and which is always on; and an anomaly detection circuit (11a).