A nuclear reactor power regulator comprising: a frequency fluctuation detection unit that is configured to detect a frequency fluctuation of at least one of an output power change command signal output from a central load dispatching center and an electric power system frequency signal output from an electric power system; a control unit that is configured to conduct control in such a way as to receive, as an input, a frequency fluctuation detection signal of the frequency fluctuation detection unit, and to output a reactor pressure adjustment command signal, which is for adjusting a reactor pressure, and a reactor recirculation flow adjustment command signal, which is for adjusting a reactor recirculation flow; a reactor pressure adjustment unit that is configured to receive, as an input, the reactor pressure adjustment command signal, and to adjust a reactor pressure adjustment start time and a pressure fluctuating range showing a range in which the pressure is allowed to change to a target pressure value; and a reactor recirculation flow adjustment unit that is configured to receive, as an input, the reactor recirculation flow adjustment command signal, and to adjust a reactor recirculation flow adjustment start time and a flow fluctuating range showing a range in which the flow is allowed to change to a target flow value, wherein the control unit is configured to output the reactor pressure adjustment command signal at a predetermined time after outputting the reactor recirculation flow adjustment command signal, the predetermined time being predetermined based on request from the electric power system. a frequency fluctuation detection unit that is configured to detect a frequency fluctuation of at least one of an output power change command signal output from a central load dispatching center and an electric power system frequency signal output from an electric power system; a control unit that is configured to conduct control in such a way as to receive, as an input, a frequency fluctuation detection signal of the frequency fluctuation detection unit, and to output a reactor pressure adjustment command signal, which is for adjusting a reactor pressure, and a reactor recirculation flow adjustment command signal, which is for adjusting a reactor recirculation flow; a reactor pressure adjustment unit that is configured to receive, as an input, the reactor pressure adjustment command signal, and to adjust a reactor pressure adjustment start time and a pressure fluctuating range showing a range in which the pressure is allowed to change to a target pressure value; and a reactor recirculation flow adjustment unit that is configured to receive, as an input, the reactor recirculation flow adjustment command signal, and to adjust a reactor recirculation flow adjustment start time and a flow fluctuating range showing a range in which the flow is allowed to change to a target flow value, wherein the control unit is configured to output the reactor pressure adjustment command signal at a predetermined time after outputting the reactor recirculation flow adjustment command signal, the predetermined time being predetermined based on request from the electric power system.