A versatile and thin headrest can be tilted lightly and reliably from a head support state to a storage state by reducing an operation load. The headrest includes a support member mounted on the upper part of a backrest seat, a frame rotatably engaged with the support member, a frame urging element(s), and a lock mechanism provided between the frame and the support member. The lock mechanism includes locking members disposed on the support member and formed with engagement groove parts, a movable operation lever having concave parts formed directed toward the support member side, fixing members pivotally supported on the frame and capable of being crossingly engaged with and disengaged from the engagement groove parts along with the movement of the operation lever, and an operation lever urging element(s) for urging the operation lever so that the fixing members are urged in the direction of the engagement groove parts.