To solve the problem that a solar power generation system installed in an individual house is not a power selling system for using a storage battery which does not depend on a type of a power generator although it transmits power from the storage battery peculiar to the power generator to a commercial power system by reverse power flow when power is sold from the storage battery incorporated in the power generator.

A portable power storage device can receive power generated by various power generators. The power selling system for selling accumulated power, which can be connected to the power generator, to which power is inputted from the power generator, in which power is accumulated in a power accumulation unit and which is connected to a power take-out device when a user desires to sell power, is provided.