PURPOSE:To improve production capacity and quality of products by extruding a strip for two beads simultaneously with wrinkles and by cutting out fin portions into desired shapes. CONSTITUTION:The width of a fin portion 12 of a suitable thickness which connects bisymmetrical pipe shaped portions 11, 11' is to be the sum of the widths of two beads. Then, rolls 21, 21' for pressing wrinkles on the right and left edges and rolls 22, 22' for pressing wrinkles on the upper and bottom sides that have been heated by electric heaters, etc. are rotated and wrinkles are made on the surfaces of pipe shaped portion. The formed product which has wrinkles on the right and left pipe shaped portions is opened by cutting with a cutter 3 in its longitudinal direction at the middle of the fin portion 12 and is separated to become two beads, one of which has a pipe shaped portion 11 and fin shaped portion 12' and the other of which has a pipe shaped portion 11' and a fin portion 12'', thus, permitting simultaneous manufacturing of two beads with wrinkles.