Abstract: A steam turbine plant of one embodiment includes a solar energy collector configured to collect solar heat, a boiler configured to change water into steam by the solar heat, a high pressure turbine including a turbine or turbines connected to each other in series, and configured to be driven by the steam from the boiler, first to N-th reheaters, where N is an integer of two or more, and first to N-th reheat turbines, wherein the first reheater is configured to heat the steam exhausted from the high pressure turbine by the solar heat, and the first reheat turbine is configured to be driven by the steam from the first reheater, and the second to N-th reheaters are configured to heat the steam exhausted from the first to (N?1)-th reheat turbines by the solar heat, respectively, and the second to N-th reheat turbines are configured to be driven by the steam from the second to the N-th reheaters, respectively.