Abstract: A control system of pumping operation comprises a cycloconverter for converting AC power from a AC power system into AC power having a given frequency, anAC exciting generator-motor, having a stator side electrically connected to the AC power system, having a rotor side electrically connected to the cycloconverter, and having a rotor shaft mechanically coupled to a pump-turbine by which the pumping operation is carried out, a circuit breaker inserted between the AC power system and the AC exciting generator-motor, a rotation speed controller for controlling a rotation speed of the AC exciting generator-motor such that the rotation speed becomes slow when the pumping operation is to be stopped, an AC excitation controller for decreasing a degree of excitation effected by the cycloconverter, wherein decreasing of the excitation degree starts when the rotation speed of the AC exciting generator-motor reaches a given minimum value, and a circuit breaker controller for turning off the circuit breaker when input po