To enable to easily and securely form an expandable opening part by expansion of an air bag, by equipping a fastener with engaging strength to be detached by deploying pressure of the air bag between peripheries of a front cloth part and side cloth parts on a air bag module equipping side.

In this post-attaching seat cover, parts between peripheries of a front cloth part and side cloth parts are formed as opening parts 3 for deployment of an air bag. The opening parts 3 are formed not by sewing those peripheries of the front cloth part 1 and the side cloth parts 2 but by equipping fasteners 4a, 4b, 4a', 4b'. A the fasteners 4a, 4b, 4a', 4b', ones with engaging strength not to be detached in ordinary uses but to be detached by the deploying pressure of the air bag are equipped. Fasteners 4a, 4b, 4a', 4b' can be sewn together by using a sewing machine.