a step of inserting a tubular parison made of a resin into an inner cavity of a mold having a first groove formed on an inner wall surface forming a part of the inner cavity;

a step of introducing a fluid into a lumen of the parison to inflate the parison such that a part of the parison enters the first groove; and

a step of removing the parison from the mold before the part of the parison reaches a bottom of the first groove, wherein the parison, to be inserted into the inner cavity of the mold, has a protruding part formed on an outer surface of the parison, the protruding part comprising a tip end portion including an end point in a radial direction of the protruding part, and a base portion that is located between the tip end portion and a balloon body, and

the parison is inflated in the cavity of the mold such that the base portion of the protruding part blocks an entrance of the first groove by coming into contact with an inner wall surface of the first groove, and the tip end portion is prevented from being contacting with the inner wall surface of the first groove.