PURPOSE: To provide a self-excitation type reactive power compensating device wherein respective single-phase inverters of three phases can generate outputs independently down to current limit values determined by their rated capacities and the sum of output current momentary values of the respective single-phase inverters of three phases need not be zero.

CONSTITUTION: A delta type stabilizing coil 10 is added as a tertiary coil to a transformer 7 for an inverter which has a star type primary coil 8 connected to the system bus 2 of a three-phase, three-wire power system and an open type secondary coil 9 where the single-phase inverters 6a, 6b, and 6c of three phases which generate inverter currents I'u, I'v, and I'w for reactive power compensation corresponding to the three-phase load current of reactive power generated by the system bus 2 are connected. The inverter-side zero-phase current of the transformer 7 circulates in this stabilizing coil 10 to inhibit the zero-phase current from flowing to the power system, thereby meeting a condition of I'u+I'v+I'w≠0.