A motor-operated valve includes a valve body having a valve chamber and a valve seat; a valve element; a valve rod for operating the valve element; a cylindrical can fixed to the valve body; a motor energizing device mounted in the outer peripheral portion of the can; a permanent magnet type rotor assembly which is supported rotatably on the inner peripheral portion of the can and is rotationally driven by the motor energizing device; a reduction gear apparatus for reducing the rotational speed of the rotor assembly; and a screw mechanism for advancing and retreating the valve element with respect to the valve seat via the reduction gear apparatus by means of the rotational movement of the rotor assembly. The rotor assembly and the reduction gear apparatus are arranged in a space defined by the valve body and the can.