Air belt device

An air belt 2B has a bag-like belt potion 10 and a knit cover 12 that surround the bag-like belt portion 10. The bag-like portion 10 has a greater width in the part that fits to the passenger's body between the shoulder and abdomen. The enlarged part of the bag-like portion 10 is folded on top of itself to form a strap-like shape. The knit cover 12 is woven so that it is expandable in the direction perpendicular to the longitudinal direction of the belt, but virtually not in the longitudinal direction. Upon activation of a gas generator 9 with a buckle 4 engaged with a tongue 5, the air belt 2B inflates. During the inflation, the length of the knit cover 12 shortens in the longitudinal direction of the belt 2B, thereby causing the belt 2B to tightly fit on the passenger's body. This ensures the proper protection of the passenger.