A power supply/demand adjusting method disclosed here is a method for adjusting power supply and demand between a power transmission/distribution system and a storage battery mounted on an electric vehicle. The method includes the steps of: acquiring power selling approval of a storage battery; acquiring battery information of a storage battery for which the power selling approval is acquired based on the acquired power selling approval and power demand information from the power transmission/distribution system; calculating a power selling amount to be transmitted from the storage battery to the power transmission/distribution system, based on the acquired battery information of the storage battery and the acquired power demand information; supplying electric vehicle based on the power selling amount from the storage battery to the power transmission/distribution system; and calculating an incentive to be provided to a user of the electric vehicle based on the power selling amount.