To provide an operating system for a reheating electric power plant capable of reducing start up time of a turbine by performing effective warming up.

This system is provided with a boiler 52, a steam turbine 51 driven by steam generated by the boiler 52, a first tube 11 for supplying steam generated by the boiler 52 to the steam turbine 51, a reheater 53, a second tube 19 for supplying steam after driving the steam turbine 51 to the reheater 53, a third tube 12 connecting the first tube 11 and the second tube 19 enabling steam generated by the boiler 52 to bypass the steam turbine 51, a valve 42 provided on the second tube 19 in passing through the steam turbine 51 for flowing out to the outside from the second tube 19, and a controlling part controlling opening of the valve 42. The controlling part 42 controls opening of the valve 42 at intermediate opening in warming up of the steam turbine 51.