To provide a manufacturing method for improving shape and accuracy of boots for a constant velocity universal joint having a shape in which an outer peripheral surface of a large diameter side fitting part is cylindrical and an inner peripheral surface has a thin wall part and thick wall part alternately in a circumferential direction.

A method includes a process of injection molding of a cup-shaped preform 41 having an intermediate part 42 connecting a large diameter side fitting part 24 and a small diameter side fitting part 25, and an occluding terminal part formed on the small diameter side fitting part 25 based on a cold parison type injection blow molding, a process of cooling the preform 41 to room temperature, maintaining it on coaxial by a large diameter side holding body 44 and small diameter side holding body 45, then heating the intermediate part 42 from outside, and a blow molding process including moving the preform 41 in a blow molding device while maintaining the holding body 44 and 45, covering the preform 41 by the blow mold 56, injecting air from an injection port 47 arranged in a shaft core position of the large diameter side holding body 44 to the shaft core position of the small diameter side holding body 25, and pressing the intermediate part 42 to the blow mold 56 to mold a bellows part 26.