PURPOSE: To prevent the entanglement of wirepins bundled in plurality by utilizing a columnal metal resistance welded at the rear end thereof as a retaining section for a resin mold.

CONSTITUTION: A wirepin 1 fixed on an electrode 12b mounted on a member 11b at the end of a shaft 5b is brought into contact with a columnal metal 2 which is larger in the diameter than the pin 1 fixed on an electrode 72b mounted on a member 71b at the end of a shaft 75b. A switch 41 is turned on with a cam 42 and on pulses of thyristers 38 and 39 are outputted alternately at respective phase angles in each of positive and negative semicycle of a power source AC waveform from a switching control circuit 40 to resistance weld the pin 1 and the metal 2. The columnal metal 2 welded on the pin 1 is utilized as retaining section for a resin mold.