PURPOSE: To enable a driving of a turbine in each driving mode of a power plant by a water supply pump by a method wherein at a time of normal start, operation is changed over from a low pressure subsidiary steam piping to a main turbine steam extraction piping to drive a water supply pump turbine, and at a time of rapid restart after stop of a generator, the operation is changed over from a high pressure subsidiary steam piping to the main turbine steam extraction piping to drive the water supply pump turbine.

CONSTITUTION: A water supplier of a power plant comprising a water supply pump turbine 8, which gives steam to a main turbine 2 to drive a generator 3 and whose water supply pump to supply water to a steam generator is driven by steam, is provided, as a steam supply pipe to drive the water supply pump turbine 8, with a main turbine steam extraction piping for leading main turbine steam extraction, a high pressure subsidiary steam piping for leading high pressure steam and a low pressure subsidiary steam piping for leading low pressure steam. At a time of rapid restart after stop of a generator, the operation is changed over from the high pressure subsidiary steam piping to the main turbine steam extraction piping to drive the water supply pump turbine 8.