Steam valve, and power generation system

A steam valve, comprising:

• a tubular stop valve, the stop valve being configured to move toward an upper end side along a direction of an axis when the stop valve is opened and move toward a lower end side along the direction of the axis when the stop valve is closed;
• and
• a valve main body configured to accommodate the stop valve,
• wherein a base end portion including an end portion of the stop valve at the upper end side in the direction of the axis is accommodated in a first accommodation space formed in the valve main body,
• wherein the base end portion has a plurality of inclination surfaces formed on an outer circumference of the base end portion, the plurality of inclination surfaces being inclined such that a distance from the axis to each of the plurality of inclination surfaces decreases toward the upper end side in the direction of the axis, and
• wherein a plurality of contact surfaces are formed in the first accommodation space to come in contact with the plurality of inclination surfaces respectively when the stop valve moves toward the upper end side in the direction of the axis.