A steam turbine plant comprising: a high-medium pressure turbine having a high-pressure turbine section provided at one end portion in an axial direction and a medium-pressure turbine section provided at the other end portion; a low-pressure turbine (22, 23) that is disposed coaxially with the high-medium pressure turbine; a condenser (33, 34) that is configured to cool steam used in the low-pressure turbine (22, 23) to condense the steam into condensate; a high-pressure feed-water heater that is configured to heat the condensate with steam discharged from the high-pressure turbine section; and a high-pressure moisture separating and heating device that is configured to remove-moisture of steam discharged from the high-pressure turbine section and to perform heating with a part of steam that is sent to an inlet portion of the high-pressure turbine section, characterized by: a low-pressure moisture separating and heating device that is configured to remove moisture of steam discharged from the medium-pressure turbine section and to perform heating with a part of steam that is sent to an inlet portion of the high-pressure turbine section and a part of steam that is sent from an outlet portion of the high-pressure turbine section to an inlet portion of the high-pressure moisture separating and heating device, and steam pipes (63, 29, 64) that are configured to send steam discharged from the high-pressure turbine section, from the outlet portion of the high-pressure turbine section to the high-pressure feed-water heater, the high-pressure moisture separating and heating device, and the low-pressure moisture separating and heating device. a high-medium pressure turbine having a high-pressure turbine section provided at one end portion in an axial direction and a medium-pressure turbine section provided at the other end portion; a low-pressure turbine (22, 23) that is disposed coaxially with the high-medium pressure turbine; a condenser (33, 34) that is configured to cool steam used in the low-pressure turbine (22, 23) to condense the steam into condensate; a high-pressure feed-water heater that is configured to heat the condensate with steam discharged from the high-pressure turbine section; and a high-pressure moisture separating and heating device that is configured to remove-moisture of steam discharged from the high-pressure turbine section and to perform heating with a part of steam that is sent to an inlet portion of the high-pressure turbine section, characterized by: a low-pressure moisture separating and heating device that is configured to remove moisture of steam discharged from the medium-pressure turbine section and to perform heating with a part of steam that is sent to an inlet portion of the high-pressure turbine section and a part of steam that is sent from an outlet portion of the high-pressure turbine section to an inlet portion of the high-pressure moisture separating and heating device, and steam pipes (63, 29, 64) that are configured to send steam discharged from the high-pressure turbine section, from the outlet portion of the high-pressure turbine section to the high-pressure feed-water heater, the high-pressure moisture separating and heating device, and the low-pressure moisture separating and heating device. a low-pressure moisture separating and heating device that is configured to remove moisture of steam discharged from the medium-pressure turbine section and to perform heating with a part of steam that is sent to an inlet portion of the high-pressure turbine section and a part of steam that is sent from an outlet portion of the high-pressure turbine section to an inlet portion of the high-pressure moisture separating and heating device, and steam pipes (63, 29, 64) that are configured to send steam discharged from the high-pressure turbine section, from the outlet portion of the high-pressure turbine section to the high-pressure feed-water heater, the high-pressure moisture separating and heating device, and the low-pressure moisture separating and heating device.