To prevent the damage of a bladder caused by the contact with a clamp pawl.

The underside inner peripheral part 4B of a ring 4 is externally fitted to the upper end outer peripheral part 6A of a body 6 and the body 6 is rotatably fitted to the ring 4. A gap δ is formed between the inclined surface 6B of the body 6 and the inclined surface 4C of the ring 4. Accordingly, the body 6 is moved forward and rearward by the gap δ in the axial line direction of a tire with respect to the ring 4. Pawls 8 are supported on the upper side inner peripheral part 4D of the ring 4 in a shakable manner at two places on the diagonal line on the same circumference of a circle by pins 9. An annular ratchet wheel 10 is fixed to the body 6 and the shevron-shaped teeth 12 locked with the pawls 8 are formed to the entire periphery of the upper end surface of the ratchet wheel 10 at an equal pitch. The pawls 8 and the teeth 12 of the ratchet wheel 10 constitute a ratched feed mechanism and the body 6 is rotated by one pitch of the teeth 12 with respect to the ring 4 by one forward and rearward movement of the body 6 to the ring 4.