The present invention provides a steam valve which controls the flowing of steam passing through the valve seat for greatly reducing pressure loss when the amount of steam flowing from a boiler into a steam turbine is controlled or switched off. A reheating steam valve (1) is configured between a steam inlet flow path (31) which guides the steam from the boiler (51) and a steam outlet flow path (32) which guides steam to an intermediate pressure turbine (59). The reheating steam valve (1) comprises the following components: an intermediate stop valve (20) which is driven from one side and can move to a preset direction; a reheating steam stop valve (21) which is connected with the other side of the intermediate stop valve (20) and is driven from the other side and can move to the preset direction; and a valve seat (9) which is formed with a hollow annular shape and abuts on the regulating valve and the stop valve when the regulating valve and the stop valve move to the other side. The other side of the valve seat (9) is provided with a projection part (10) which projects into the steam outlet flow path (32).