SEAT

A seat on which an occupant of a vehicle is seated includes: a backrest that faces a back part of the occupant; a headrest provided in an upper part of the backrest; a backrest frame including side members that extend in an upward-downward direction along left and right side end parts of the backrest; a cross member provided to bridge the left and right side members and attached to the side members to be movable upward and downward; a headrest post that protrudes downward from the headrest and is coupled to the cross member; and a cross member detachment mechanism performs detachment of the cross member from the side members, in accordance with a load toward a rear side of the vehicle input to the cross member. The load triggering the detachment by the cross member detachment mechanism decreases as the cross member rises with respect to the side members.