A power management server includes a receiver configured to receive an adjustment message for adjusting a supply-demand balance of a power system; a management unit configured to manage two or more apparatuses; a controller configured to determine individual adjusted power amounts each adjusted by a respective one of the two or more apparatuses and start timings at each of which a respective one of the two or more apparatuses starts power adjustment so that a total adjusted power amount requested via the adjustment message is adjusted; and a transmitter configured to transmit a control message including an information element specifying the individual adjusted power amounts and the start timings. The controller determines the start timings that are different from each other and each of which is for a respective one of the two or more apparatuses.