PURPOSE: To miniaturize a seat belt anchor gusset by fixing the seat belt anchor gusset to a front funnel inside the blocked section structure of a front tunnel.

CONSTITUTION: A tunnel side member 11 is extended in the longitudinal direction of a car body, inside a front tunnel 2. This tunnel side member 11 is welded to the front tunnel 2 so as to constitute blocked section structure inside the front tunnel 2. By the blocked section structure 12, the structural reirnforcement of a seat belt anchor part 14 is materialized. Accordingly, even if excessive load is applied to the seat belt, the deformation of the seat belt anchor part 14 does not become so larger, so the miniaturization and the weight reduction of the seat anchor belt can be materialized.