Abstract: A headrest holder includes two tension pieces defined in the body portion thereof and a head portion. The two tension pieces, each including a protrudent portion, are spaced apart from each other along the longitudinal direction of that body portion, while being in a mutually facing relation, so that a headrest stay inserted in the headrest holder is retained between the two protrudent portions against wobbling. Further, those two tension pieces and either the head portion or a support bracket of seat frame establish three supportive points. Namely, the headrest holder inserted in the support bracket is retained against wobbling because the two protrudent portions and the headrest holder's neck portion closely contact the support bracket. Also, a headrest stay inserted in the headrest holder is retained against wobbling because the two protrudent portions and headrest holder's head portion closely contact the headrest stay.