To enhance the performance of penetrating a stay through a trim cover when a headrest with an opening has the stay with a part which is penetrated through the trim cover and has a wide width in comparison with the width between both legs.

Penetrating parts (H) (H) where the stay (B) is penetrated from the bottom of the trim cover (A) are place at a part (1) to join plural outer cover pieces (10) (11) constituting the trim cover (A). The penetrating parts (H) (H) are made up of trapezoidal protruding pieces (12) (22) which are extended from margins for the parts (1) to join and are overlapped, and are sewed up together along the right and left ends of the protrusion.