In a chargeable-and-dischargeable power supply system, a plurality of battery cell sections are connected in series with one another, a plurality of cell state detecting sections are installed for the respective battery cell sections and configured to detect a charge state in the respectively corresponding battery cell sections, a power control section is configured to carry out a power supply control for the battery cell sections, a first electrical isolation section is installed in a first signal route from the power control section to one of the cell state detecting sections which is for a highest potential positioned battery cell section, and a second electrical isolation section is installed in a second signal route from one of the cell state detecting sections which is for a lowest potential positioned battery cell section to the power control section.