PURPOSE: To impart a sufficient rigidity to the mounting part of an air bag cover solidly formed with plastics for lightweightiness to the body as well as to facilitate the manufacture so easy enough.

CONSTITUTION: A plastic air bag cover 1 conceals an air bag storage part of a vehicle. This air bag cover 1 sets an upper end 2 down to a locking spot with a body and uses it as a hinge part at time of unfolding an air bag. This upper end 2 is provided with a bolt hole 6, while there are provided wall parts 8, 9 forming an open section where a plate core 3, having a bolt hole 4, is insertable through so as to be sewn.