A casing for housing an occupant protection device unit is composed of a metallic base with its plate surfaces facing upward and downward, respectively, and a main body that is put on and mounted on the surface of the base. A bracket formed integrally with the base is composed of a plate-like leg extending laterally from the edge in the base and a fastening member that is integrally formed at an end of the leg and is bolted to the vehicle body. The leg is composed of a through-hole vertically passing therethrough and the two weak portions. The two weak portions are composed of two branching portions separated by the through-hole in the leg. If an excessive collision load is exerted on the bracket from the vehicle body, the two weak portions are torn off, thereby allowing the occupant protection control unit to be protected.