PURPOSE: To control a power system stably by controlling the total reactive power of a power capacitor and a cycloconverter depending on the load and schedule thereby improving power factor.

CONSTITUTION: Reactive power generated from a cycloconverter 3 during steady operation is calculated in order to determine the number of power capacitor facilities 10 to be connected with a power supply system. The reactive power controller comprises a reactive power reference operating unit 9 for calculating reactive power to be generated from the cycloconverter upon stoppage of some AC motors 5 and determining the number of required power capacitor facilities, and an automatic throw-in unit 12 for commanding throw-in of the capacitor facility such that fluctuation of system voltage is minimized. The reactive power controller further comprises a unit 13 for operating distribution of reactive power from the cycloconverter such that the total sum thereof will be constant during operation of the motors, and a reactive power controller 14 for controlling the rotational speed of AC motors such that the reactive power generated from the cycloconverter will match with a reactive power reference.