PURPOSE: To obtain control equipment of a reactor power which ensures the water level of a reactor and controls the reactor power automatically and safely, by providing a recirculation from an injection piping of a high pressure injection system to a pressure control chamber pool and a flow control device and by injecting a high pressure injection flow corresponding to the water level of the reactor set beforehand, from the high pressure injection system, when scram fail transient phenomena take place.

CONSTITUTION: An injection piping 15 of a high pressure injection system connected to a feed water piping 3 and a high pressure injection recirculation system branching from this injection piping 15 of the high pressure injection system, communicating with a pressure control chamber room 7 and being equipped with a flow regulating means 20 are provided. By controlling the flow regulating means 20 by a power control device 23 comprising a scram fail transient phenomenon determining part, a high pressure injection system needed injection flow calculating part and a control signal calculating part, a flow rate of feed water to a reactor at the time when scram fail transient phenomena of the reactor take place is controlled.