To increase a power storage amount with the reduction of an environmental load, to suppress the consumption of stored power by simple system implementation with mutual coordination, and to increase a drivable load device with an elongated drive time.

A power storage device includes changeover switches 31, 32 to enable connection of one of external input terminals 11-13 to a secondary battery 43, a changeover switch 51 and switches 61, 62, 64, 65 to enable connection of one of the external terminals 11-13 and the secondary battery 43 to one of external output terminals 71, 72; and a system controller 80 for controlling to store high priority power into the secondary battery 43, and to output to the output terminals 71, 72 higher priority power out of the power input to the external input terminals 11-13 and the power stored in the secondary battery 43.