A valve control system for a steam turbine that decrease in effective power as well as secure control stability in the event of an electric power system accident is provided.A valve control system for a steam turbine includes an accident detection unit 44 which detects an occurrence of an electric power system accident, a first selection unit 45 which selects, from a plurality of control valves 13 (13a˜13d) which adjust a volume of steam flowing into a steam turbine, control valves 13 to be rapidly closed according to a scale of the accident detected, and a normal control circuit 11 which continues normal pressure or speed control by the control valves 13 which are not selected.