A jack with a switch includes a square-sectioned body of an insulating resin material which has on its front a cylindrical sleeve for receiving a plug, and an open rear end. The body has an internal regulating rib molded integrally therewith and extending from the rear end of the sleeve toward the rear opening of the body through a hole made in a leaf contact piece, for limiting inclination of a plug inserted into the body. An L-shaped lug is inserted into the body through its rear opening so that the tip of the plug is gripped by top and bottom contact pieces extending from the lug. A separator, inserted into the body through its rear opening, has a U-shaped base portion for receiving the tip end portion of the plug and a pair of movable pieces extending from right and left end portions of the base toward the sleeve. When the plug is inserted, the movable pieces are displayed outwardly in opposite directions to thereby turn ON or OFF contact piece switches formed in the body, and at the same time the tip end portion of the plug is received by the U-shaped base portion of the separator, by which lateral movement of the plug is prevented. A rotatable cover is molded integrally with the body along one marginal edge of the rear opening to cover the opening.