A method for mounting a waterproof plug to the front end of a covered electric wire, comprising the steps of feeding waterproof plugs to a first position of a transfer path one by one from a magazine in such a manner that the opening of each waterproof plug is in parallel with the transfer path; feeding a covered electric wire to a mounting position as a second position of the transfer path in an uncovered state of the front end thereof; and transferring the waterproof plug from the first position to the second position and inserting the uncovered end of the electric wire into the opening of the waterproof plug. Also disclosed is an apparatus for mounting a waterproof plug to the front end of a covered electric wire, including means for feeding waterproof plugs to a first position of a transfer path one by one in such a manner that the opening of each waterproof plug is in parallel with the transfer path; means for feeding a covered electric wire to a mounting position as a second position of the transfer path in an uncovered state of the front end thereof; and means for transferring the waterproof plug from the first position to the second position and inserting and clamping the uncovered end of the electric wire into the opening of the waterproof plug.