A nuclear reactor power regulator adjusts reactor output based on a reactor output target value and a reactor output change rate. The regulator includes a reactor output calculating device that performs computation based on a thermal equilibrium from power signals of plant parameters to calculate a reactor output signal. A correcting device corrects a continuously obtained reactor output equivalent signal that is considered to be equivalent to a reactor output at a calculation interval of the output signal, so that the output equivalent signal coincides with the output signal. The correcting device calculates a continuous corrected output equivalent signal. A reactor output controlling device calculates a reactor output control signal for controlling the output of the reactor, using the corrected reactor output equivalent signal, the reactor output target value, and the reactor output change rate. A reactor output controller is operated based on the reactor output control signal.