To prevent a stick of a valve rod caused by the followings: a difference of linear expansion coefficients between a guide member and a bush of a steam valve device causes an oxide scale S to be laminated between the guide and the bush; the laminated oxide scale S while a valve is cold causes an inner diameter of the bush to largely contract; and the bush tightens the valve rod.

The steam valve device includes a groove 91 having any inclination angle θ at an outer periphery of the bush 9 so that the outer periphery which serves as a fitting surface from the guide member 8 to the bush 9 elastically deforms when the oxide scale S laminated between the guide member 8 and the bush 9 while the valve device is cold causes the fitting interference relative to the bush 9 of the guide member 8 to increase.