The present invention is one that heats the inside of the spinning pack in a short period of time while keeping temperature of an outer circumferential part of a spinning pack less than a maximum allowable temperature, and provided with: a magnetic path forming member that forms a magnetic path with a spinning pack arrangement space where the spinning pack is arranged to occupy the space and be positioned intermediate respective ends of the magnetic path forming member that border the space; and a magnetic flux generating winding that is provided so as to be wound to surround the spinning pack arrangement space.