The pillar garnish has a main body, an extension part that is formed integrally with the main body, including a guide surface at an upper end of the extension part, the guide surface controlling a direction in which the air bag apparatus is unfolded so that the air bag apparatus is unfolded into the interior of the vehicle when the air bag apparatus is inflated, and a box portion that is formed integrally with the main body and the extension part, the box portion being positioned between the main body and the pillar. The box portion has a back wall portion and a pair of side wall portions that are adjacent to the back wall portion and the main body. The side wall portion has a thick portion and a thin portion, the thin portion being disposed closer to the main body than to the back wall portion.