Provided is a pneumatic tire vulcanizing method which includes the steps of setting a green tire in a mold, inserting a bladder inside the green tire, and expanding the bladder to press the bladder to an outer side in the tire radial direction and perform vulcanization molding. The bladder is expanded with a rigidity reinforcement ring interposed between an inner circumferential surface of a region of the green tire corresponding to a tread portion and an outer circumferential surface of a region of the bladder corresponding to the tread portion.