The grid interconnection system is provided with a switching unit configured to switch a connection destination of an interconnection terminal of a first power conditioner and a load, between a power grid and a self-standing terminal of a second power conditioner, and a connection controller configured to execute, on the switching unit, first control for connecting the power grid to the interconnection terminal of the first power conditioner and the load in a non-power outage of the power grid, and second control for connecting the self-standing terminal of the second power conditioner to the interconnection terminal of the first power conditioner and the load in a power outage of the power grid.