A power supply device includes battery equipment and voltage detecting circuitry. The battery equipment includes positive-side and negative-side battery blocks that are connected to each other at a reference midpoint. The voltage detecting circuitry detects the respective voltage values of serially-connected battery modules of the battery equipment. The voltage detecting circuitry includes positive-side and negative side voltage management ICs with respect to the reference midpoint. The positive-side and negative side voltage management ICs manage the voltage conditions of the battery modules in the positive-side and negative-side battery blocks, respectively. Positive-side and negative-side voltage power lines of each of the positive-side and negative side voltage management ICs are connected to positive-side and negative-side output terminals of the battery equipment so that all the battery modules supply electric power to each of the voltage management ICs. The voltage management ICs have a common ground line.