To operate a valve completely electrically, and to operate the same in a closing direction at the time of emergency cutting-off.

A valve for a steam turbine is composed of a valve body 24, a valve box 12 having a valve seat 25, a valve rod 22 for operating the valve body 24, and a driving mechanism 14 for operating the valve rod 22. The driving mechanism includes a motor 16, an electromagnet joint 18, a ball screw 20 and an accumulator 28. A bush 20a constituting the ball screw 20 is connected through the electromagnet joint 18 to the motor 16, and the tip part of a rod 20b constituting the ball screw 20 is connected to the base part of the valve rod 22. Further, a flange portion 26 is formed in the tip part of the rod 20b, and the accumulator 28 is incorporated between the flange portion 26 and the bush 20a.