PURPOSE: To prevent the failures in the appearance, joining and shriveling shape of a bottom part by heating the part of a pipe to be the bottom part of a molding body, and performing a stretch forming by converging and contracting respective layers of the heating part into a plurality of wrinkles, and then after fusion-combining, cooling and solidifying them.

CONSTITUTION: A pipe 6 equal to at least two pieces or more of a molding body is supported by supporting devices 13, 14, 15, and also capable of being turned. The boundary part as the part to be heated of the pipe 6 is heated from the inner part by an infrared heater capable of coming in and out being turned, and heated by a heating and cooling device 10 positioned outwards. After finishing the heating and aging for a while, it is press-worked from the outside by press molds 11 provided at a plurality of positions, and performed a converging and contracting stretch forming into wrinkle shapes, so that the bottom part equal to two molding bodies is worked simultaneously. After cooling and fixing, the molds 11 are separated, and the bottom boundary 16 and the mouth part boundary 17 are cut away with the result that two molding bodies are obtained. The molding bodies 6-1, 6-2 are taken away, afterwards, a new pipe is forwarded by the supporting devices so as to start the next cycle molding.