A seat belt system includes a storage case including a main body having a box shape and a storage portion, the main body having an opening formed thereon through which first and second tongues are inserted, the first tongue being attached to an end of a belt and to be connected to a first buckle on a seat side, the second tongue being movably attached to the belt and to be connected to a second buckle on the seat side, and a storage portion formed in a shape tapered in an insertion direction of the first and second tongues, protruding from the main body and including first and second inclined surfaces that are formed on both sides of a surface opposite a surface having the opening formed thereon and are inclined to guide insertion of the first and second tongues.