PURPOSE: To form a uniform wall thickness covering an entire receptacle, by dividing a wall thickening process of the receptacle into two stages, thickening beforehand the wall of a tip part of the receptacle, then thickening the wall of a following part of the receptacle.

CONSTITUTION: A wall thickening part is beforehand shaped at a tip part (a) of a straight pipe 4 of a plastics pipe P. Then, an inner mold A is inserted after an entire end part of the pipe is heat-softened, the inner mold is expanded in its diameter and a receptacle is shaped. After that, the outer molds B, C are clamped and the pipe P is forced in from the behind (a direction of an arrow), then a wall of a following part (b) which is not yet thickened is made thick to the same thickness as the wall of the tip part (a) which is thickened already.