To simplify the mechanism of an occupant protection system in which a seat bag at the front part of a seat cushion and a lap bag are inflated to protect an occupant and also to simplify the mounting structure of the occupant protection system to a seat frame, a holder is mounted to the side frame of a seat. The holder includes a pretensioner connected to a lap anchor, an inflator for inflating a seat bag and a lap bag, and a manifold for distributing gas from the inflator to the seat bag and the lap bag. The connecting structure of the lap anchor and the pretensioner is of a latch type (insert-lock type).