A power flow control system is provided that is capable of improving the reliability of controlling power flow fluctuation and creating wide applicability for systems that control power flow fluctuation. A power-varying device (101) varies the distribution line power amount, which is a value of the power flow that flows in a distribution line (112) to which is connected a plurality of power sources (111) that each generate power. A measurement device (102) measures an index value relating to the total generated power amount, which is the sum total of the amount of power generated by each of the power sources. A calculation device (103) estimates the total generated power amount from the index value, and according to the estimation result, regulates the amount of change in the distribution line power amount that is changed by the power-varying device.