Abstract: A cord tension device for use in plug making machine for forming a plug and a cord protector integrally on one end of electric cord. The plug making machine has a mold device having a plurality of mold cavities for receiving the cord ends and a holding device for holding the plug terminals and cord ends in the right places within the mold device. The cord tension device has a clamp device which is adapted to clamp the cord portion projecting out of the mold device and a driving device adapted to drive the clamp device away from the mold device thereby to impart a tension to the cords received by the mold device. In consequence, the cord ends are located and set correctly along the axes of the mold cavities under application of tension, so that the cord protector is formed to have a uniform thickness distribution in the circumferential direction.