A rotary encoder includes a rotary encoding unit attached to a rotary shaft which is rotatably held in a metal casing, a number-of-revolution detection unit supported by the metal casing for detecting a number of revolutions of the rotary encoding unit and producing heat, a cylindrical insulating resin cover having a base end attached to the metal casing for accommodating therein the rotary encoding unit and the number-of-revolution detection unit, a metal lid for blocking an opening of the other end of the insulating resin cover, and a shield cable electrically connected to the number-of-revolution detection unit and drawn out from a cable outlet of the metal lid. A shield of the shield cable is heat-transferably and electrically connected to the metal lid.