A reactive power control apparatus for an AC power system includes a reactive power compensation device, a compensation capacitor device and a compensation capacitor control device. The compensation capacitor control device includes a detection voltage output circuit which outputs a bus detection voltage after the clearing of a voltage drop abnormality, corresponding to the AC voltage of a system bus after the voltage drop abnormality that occurred in the AC power system has been cleared, and a compensation capacitor control circuit which controls the connection status of a compensation capacitor with respect to the system bus. The compensation capacitor control circuit controls the connection status of the compensation capacitor with respect to the system bus, on the basis of the voltage level of the bus detection voltage after the clearing of the voltage drop abnormality.