To provide a power storage device for improving charging efficiency at the time of storing supply power fluctuating with time.

The power storage device includes a main power storage part 11 comprising a secondary battery, an auxiliary power storage part 12 which can be connected in series to the main power storage part 11 and contains an electric double layer capacitor and a control part 13 switching a state where supply power is supplied to the main power storage part 11 or the auxiliary power storage part 12 and a state where supply power is supplied to the main power storage part 11 and the auxiliary power storage part 12, which are connected in series, in accordance with fluctuation of supply power.

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