A server configured to manage electric power of a first power grid, the first power grid being configured to be connected to and disconnected from a second power grid, the server comprising: a resource manager configured to manage a plurality of power adjustment resources electrically connectable to the first power grid; and a first switching unit configured to switch the first power grid from an isolated operation to a grid-connected operation, the first power grid being interconnected with the second power grid in the grid-connected operation, the first switching unit being configured to, in switching the first power grid from the isolated operation to the grid-connected operation, determine a master and a slave among the plurality of power adjustment resources, and allow the first power grid to be connected to the second power grid after master-slave control by means of the master and the slave such that electric power of the first power grid is in synchronization with electric power of the second power grid, characterized in that the first switching unit is configured to preferentially select as the master, a power adjustment resource close to a point of connection between the first power grid and the second power grid from among the plurality of power adjustment resources, in that the first switching unit is configured to select the master based on communication performance and output performance of the power adjustment resource, and in that the first switching unit is configured to exclude a first power adjustment resource and a second power adjustment resource from power adjustment resources that are responsive to a synchronization command, the first power adjustment resource having a communication rate lower than a first threshold value, the second power adjustment resource having maximum output power lower than a second threshold value, and select as the master, one power adjustment resource closest to the point of connection from among remaining power adjustment resources after the exclusion. a resource manager configured to manage a plurality of power adjustment resources electrically connectable to the first power grid; and a first switching unit configured to switch the first power grid from an isolated operation to a grid-connected operation, the first power grid being interconnected with the second power grid in the grid-connected operation, the first switching unit being configured to, in switching the first power grid from the isolated operation to the grid-connected operation, determine a master and a slave among the plurality of power adjustment resources, and allow the first power grid to be connected to the second power grid after master-slave control by means of the master and the slave such that electric power of the first power grid is in synchronization with electric power of the second power grid, determine a master and a slave among the plurality of power adjustment resources, and allow the first power grid to be connected to the second power grid after master-slave control by means of the master and the slave such that electric power of the first power grid is in synchronization with electric power of the second power grid, characterized in that the first switching unit is configured to preferentially select as the master, a power adjustment resource close to a point of connection between the first power grid and the second power grid from among the plurality of power adjustment resources, in that the first switching unit is configured to select the master based on communication performance and output performance of the power adjustment resource, and in that the first switching unit is configured to exclude a first power adjustment resource and a second power adjustment resource from power adjustment resources that are responsive to a synchronization command, the first power adjustment resource having a communication rate lower than a first threshold value, the second power adjustment resource having maximum output power lower than a second threshold value, and select as the master, one power adjustment resource closest to the point of connection from among remaining power adjustment resources after the exclusion. exclude a first power adjustment resource and a second power adjustment resource from power adjustment resources that are responsive to a synchronization command, the first power adjustment resource having a communication rate lower than a first threshold value, the second power adjustment resource having maximum output power lower than a second threshold value, and select as the master, one power adjustment resource closest to the point of connection from among remaining power adjustment resources after the exclusion.