To efficiently correct the knee/leg parts of the bow-legs where the left/right knee leg parts are mutually bent outward by applying an oppression force by pneumatic pressure thereto.

An inflatable air bag body 1 communicated with an air feed/exhaust device 11 via an air feed/exhaust pipe 12 is provided with a bag central part 3 projecting to the center of a bag bottom part 2, knee/leg parts storage recess parts 5 formed between bag side parts 4 projecting to the both sides of the bag bottom part 2, and a sheet type closure part 6 having one end side edge part connected to the bag side parts 4 so as to close the upper part opening side of the knee/leg parts storage recess part 5 and the other side edge part fastened by a connecting means 7 in the upper side position of the bag central part 3. The connecting means 7 is formed of a sliding fastener or a male/female hook-and-loop fastener and the air bag body 1 is disposed with a plurality of reinforcing parts 8 into a bridging state so as to prevent the fracture of the air bag body 1 beforehand in inflating by air feed. The ratio of the lateral width intervals d1 and d2 of the bag central part to the bag side part 4 is set to 7:10.