A method of manufacturing a pneumatic tire via vulcanization of a green tire with a cylindrical vulcanization bladder inserted therein by inflating the vulcanization bladder in a mold attached to a vulcanization device to a predetermined vulcanization internal pressure to press the green tire against the mold while the green tire is being heated at a predetermined temperature, the method comprising the steps of: placing a bladder device including the vulcanization bladder at a holding position outside the mold; inserting the vulcanization bladder in the green tire with a tire axis central position of the green tire and a shaft central position of the vulcanization bladder aligned, and aligning a central position in a tire width direction of the green tire and a central position in a shaft direction of the vulcanization bladder; in a state positioned as such, supporting the green tire with the vulcanization bladder by inflating the vulcanization bladder to a predetermined green tire supportable internal pressure and bringing the vulcanization bladder in contact with an inner surface of the green tire; transporting the green tire together with the bladder device placed at the holding position to the vulcanization device and setting the green tire together with the bladder device in the mold; and inflating the vulcanization bladder to the predetermined vulcanization internal pressure, which is higher than the predetermined green tire supportable internal pressure, the method being characterized in that the bladder device is placed at the holding position with the shaft direction of the vulcanization bladder parallel to a vertical direction; the vulcanization bladder is inserted in the green tire while the green tire is suspended with an upper bead portion (Bu) of the green tire on its side supported by an arm portion of a positioning device; and upon insertion, the central position in the tire width direction of the green tire and the central position in the shaft direction of the vulcanization bladder are aligned via vertical movement of the positioning device being controlled on the basis of the central position in the tire width direction of the green tire successively detected from a side direction of the suspended green tire by a position sensor and the central position in the shaft direction obtained beforehand of the vulcanization bladder of the bladder device placed at the holding position, and wherein three or more vertical distance sensors are provided on the positioning device; a levelness of the green tire is obtained on the basis of vertical distances to the suspended green tire detected by the vertical distance sensors; and on the basis of an obtained result, the suspended green tire is kept within a preset levelness tolerance range and the central position in the tire width direction of the green tire and the central position in the shaft direction of the vulcanization bladder are aligned. placing a bladder device including the vulcanization bladder at a holding position outside the mold; inserting the vulcanization bladder in the green tire with a tire axis central position of the green tire and a shaft central position of the vulcanization bladder aligned, and aligning a central position in a tire width direction of the green tire and a central position in a shaft direction of the vulcanization bladder; in a state positioned as such, supporting the green tire with the vulcanization bladder by inflating the vulcanization bladder to a predetermined green tire supportable internal pressure and bringing the vulcanization bladder in contact with an inner surface of the green tire; transporting the green tire together with the bladder device placed at the holding position to the vulcanization device and setting the green tire together with the bladder device in the mold; and inflating the vulcanization bladder to the predetermined vulcanization internal pressure, which is higher than the predetermined green tire supportable internal pressure, the method being characterized in that the bladder device is placed at the holding position with the shaft direction of the vulcanization bladder parallel to a vertical direction; the vulcanization bladder is inserted in the green tire while the green tire is suspended with an upper bead portion (Bu) of the green tire on its side supported by an arm portion of a positioning device; and upon insertion, the central position in the tire width direction of the green tire and the central position in the shaft direction of the vulcanization bladder are aligned via vertical movement of the positioning device being controlled on the basis of the central position in the tire width direction of the green tire successively detected from a side direction of the suspended green tire by a position sensor and the central position in the shaft direction obtained beforehand of the vulcanization bladder of the bladder device placed at the holding position, and wherein three or more vertical distance sensors are provided on the positioning device; a levelness of the green tire is obtained on the basis of vertical distances to the suspended green tire detected by the vertical distance sensors; and on the basis of an obtained result, the suspended green tire is kept within a preset levelness tolerance range and the central position in the tire width direction of the green tire and the central position in the shaft direction of the vulcanization bladder are aligned.