To make the change of reactive power controllable for a load, with a power control converter of small capacity.

A reactive power compensating device detects the load current of an electric power system, detects the reactive current components contained in the load current with a coordinate transformation system 11, and controls a semiconductor power converter 4 connected to the electric power system with a current control system 17. In this device, by applying a high-pass filter for the reactive current component, the fluctuated portion, AC component of the reactive power, is compensated, and the fluctuations in the load reactive power is controlled with a power converter of small capacity. By combining this reactive power compensating device with a conventional reactive power compensating device of low-speed and large capacity, for example, phase leading capacitor, the reactive power that does not change is compensated with the reactive power compensating device of low-speed and large capacity, and it is possible to compensate for the fluctuated portion of the reactive power at high speed with the reactive power compensating device, by means of the semiconductor power converter 4.