A steam turbine includes a turbine body; a steam flow passage; a regulating valve which regulates opening and closing of the steam flow passage with a linear motion; a switching drive mechanism which drives the regulating valve; an electronic governor which controls at least the switching drive mechanism; and a controller unit. The switching drive mechanism has an electric motor which rotates when supplied with power, a conversion mechanism which converts a rotary motion of the electric motor into a linear motion of the regulating valve, and a brake which brakes the rotary motion of the electric motor. At least one of the controller unit and the electronic governor performs control such that the brake is actuated and the position of the regulating valve is maintained when at least one of the electric motor and the controller unit breaks down.