A steam turbine includes a turbine main body having blades supported rotatably, a steam channel which is connected to the turbine main body and in which steam flows, a regulating valve configured to linearly move to adjust opening/closing of the steam channel, and an opening/closing drive mechanism configured to drive the regulating valve. The opening/closing drive mechanism includes an electric motor configured to rotate by an electric power being supplied, a conversion mechanism configured to convert rotational motion of the electric motor into linear motion of the regulating valve, and a brake operated by regenerative energy of the electric motor.