A power information management system comprising: a supply information acquisition unit configured to acquire an amount of supplied power correlation correlating with an amount of externally-supplied power, which is an amount of power supplied to an external by a power supplier/demander having at least one of a power generation apparatus and a power storage apparatus; a receipt information acquisition unit configured to acquire an amount of received power correlation correlating with an amount of externally-received power, which is an amount of power received from an external by the power supplier/demander; and an available amount determination unit configured to determine an amount of available power correlation that can be available by the power supplier/demander, the amount of available power correlation correlating with an amount of power that can be used, profited or disposed by the power supplier/demander, wherein the available amount determination unit is configured to determine the amount of available power correlation at a specific point of time, based on A) the amount of supplied power correlation, B) the amount of received power correlation, and C) information about an elapsed time period from i) a point of time at which the power supplier/demander supplies power to an external, or ii) a point of time at which a difference between the amount of supplied power correlation and the amount of received power correlation meets a preset first condition to the specific point of time, characterized in that the available amount determination unit comprises a correction amount determination unit configured to determine, based on the information about the elapsed time period, a correction amount to correct the amount of available power correlation, and the correction amount determination unit is configured to determine the correction amount so that the longer the elapsed time period is, the smaller the corrected amount of available power correlation is. a supply information acquisition unit configured to acquire an amount of supplied power correlation correlating with an amount of externally-supplied power, which is an amount of power supplied to an external by a power supplier/demander having at least one of a power generation apparatus and a power storage apparatus; a receipt information acquisition unit configured to acquire an amount of received power correlation correlating with an amount of externally-received power, which is an amount of power received from an external by the power supplier/demander; and an available amount determination unit configured to determine an amount of available power correlation that can be available by the power supplier/demander, the amount of available power correlation correlating with an amount of power that can be used, profited or disposed by the power supplier/demander, wherein the available amount determination unit is configured to determine the amount of available power correlation at a specific point of time, based on A) the amount of supplied power correlation, B) the amount of received power correlation, and C) information about an elapsed time period from i) a point of time at which the power supplier/demander supplies power to an external, or ii) a point of time at which a difference between the amount of supplied power correlation and the amount of received power correlation meets a preset first condition to the specific point of time, characterized in that the available amount determination unit comprises a correction amount determination unit configured to determine, based on the information about the elapsed time period, a correction amount to correct the amount of available power correlation, and the correction amount determination unit is configured to determine the correction amount so that the longer the elapsed time period is, the smaller the corrected amount of available power correlation is.