In one embodiment a relief safety valve driving system that supplies a driving gas by use of a relief safety valve driving unit and thereby opens a relief safety valve provided in a main steam system of a nuclear power plant if an accident or a transient state occurs, for protecting a reactor against pressurization, wherein the relief safety valve driving unit opens the relief safety valve by supplying the driving gas to the relief safety valve by one or more auto-depressurization system actuating signals, among auto-depressurization system actuating signals respectively belonging to three safety segments, or by a relief valve functions actuating signal, and closes the relief safety valve without supplying the driving gas thereto when none of the auto-depressurization system actuating signals and the relief valve functions actuating signal is generated.