A manufacturing method of an insulation cap, includes the steps of: supplying an elongated tube from a tube supplying unit to a tube placing table; moving a tube press-fastening portion and a welding body portion towards the tube placing table so as to press-fasten a press-fastening position of the tube placed on the tube placing table and to press-contact a press-contacting position of the tube placed on the tube placing table; performing a welding process with respect to the press-contacting position of the tube; moving the tube placing table during the welding process to feed the tube in a tube feeding direction by a specified amount; blanking the tube subjected to the welding process after feeding the tube to form the insulation cap; and discharging the formed insulation cap from a blanking position.