A nuclear power control system includes: a safety protection apparatus which outputs a first safety mode operating signal while outputting a first unsafety mode operating signal; a CCF apparatus that outputs a second safety mode operating signal; and a signal input/output circuit that is connected to the safety protection apparatus and the CCF apparatus. The signal input/output circuit includes an OR circuit that outputs a third safety mode operating signal based on the presence or absence of an input of the first safety mode operating signal and the second safety mode operating signal; a NOT circuit that is connected to the output side of the OR circuit; and an AND circuit that outputs a third unsafety mode operating signal, and the presence and absence of an input of a first unsafety mode operating signal.