A control device for a plurality of distributed generators connected to a main grid, the control device including a load power measuring unit measuring power consumption of loads connected to the plurality of distributed generators, a distributed generator power measuring unit measuring power output from the plurality of distributed generators, a power flow reference value determining unit determining a power flow reference value of a power line connected to the main grid based on the power consumption and the power output from the plurality of distributed generators, and a mode control unit changing an operation mode of one of the plurality of distributed generators such that a flow power of the power line connected to the main grid maintains the power flow reference value.