An air belt apparatus for use in a vehicle is provided to improve the comfort of the webbing during normal operation by thinning the webbing that passes through a shoulder anchor, while extending a developing length of an expanding portion upward when the expanding portion is expanded. The air belt apparatus includes webbing corresponding to the chest of an occupant, an expanding portion provided in the webbing, and folded back so as to be developed up to a position corresponding to a head of the occupant at a time of expansion, and an extending portion covering the expanding portion and extended upward from an upper end of the expanding portion, and further includes an elastic cover being expandable along the expansion of the expanding portion, and a non-extendable sheet member that enables the extending portion to pass through the shoulder anchor by reinforcing the extending portion of the elastic cover.