A seat belt apparatus for a vehicle including an anchor metal plate coupled with a vehicle body by a fastening bolt to extensively support a seat belt and upper and lower covers to receive the anchor metal plate. A contact rib is formed on at least one side portion of the inner surface of the upper cover, and a sidewall is formed on a side portion of the lower cover to make contact with the contact rib. An arc-type rib is formed on the bottom plate of the lower cover corresponding to an outer peripheral portion of at least one side portion of the base portion of the anchor metal plate, and a connection rib is formed between the arc-type rib and the sidewall. An arc-type slot is formed on the bottom plate of the lower cover.