PURPOSE: To promote the simplification of piping work for a bathtub or the like by integrally molding a straight pipe part and a T-shaped pipe continuing to the former together, and disusing any connection between the straight pipe and a tee-joint.

CONSTITUTION: A polybuten parison 37 extruded out of an extrusion nozzle 36 is inserted into two straight pipes 15, 16, a bellows pipe part 19, a T-shaped pipe part 17 and two forming dies 34, 35 formed with a cavity 33 equivalent to a curved pipe part 18. When compressed air is blown into this parison 37, it is expanded and coated to a wall surface of the cavity 33, thereby securing a piping molding product in a state of having closed a tip 17a of the T-shaped pipe part 17 and another tip 18a of the curved pipe part 18, and thus an elbow and a Tee T-shaped pipe joint are disused. With this constitution, troublesome heat deposition work is omissible, and thus any piping work for a bathtub or the like is easily performable.