PURPOSE: To prevent excessive drop in the water level of a nuclear reactor under the state of stoppage of one high pressure condensate pump by providing an arithmetic device with a limiter to limit a turbine speed demand signal according to different speed set values determined by the number of operating units of low pressure and high pressure condensate pumps in a condensate system.

CONSTITUTION: For example, when one of low pressure condensate pumps stops, a protection circuit works to stop one of two each of high pressure condensate pumps and supply water pumps. At this point, in a main controller 15, a deviation becomes larger between a nuclear reactor water level signal (d) computed by a deviation detecting section 22 and a set value signal by a water level setting device 23 and a speed demand signal (f) to be outputted from a proportional integration control arithmetic device 24 increases. During the period, in a limiter 25, a switching signal is outputted from a switch 33 under the conditions of keeping an spare device from starting and a contact 28 is closed. At this point, the limiter 25 limits the upper limit of an output with a low value selector 32 based on a third control value from a third setting device 28.