Patent ID: 8444220

Claim:
A vehicle seat comprising: a headrest; a seat back having thereinside a back frame which includes an upper frame adapted to support the headrest, and a pair of side frames disposed on respective ones of right and left sides of the upper frame; an elastic member extending in a widthwise direction of the vehicle seat to interconnect the pair of side frames; a movable member provided on the elastic member, the movable member having a base portion attached to the elastic member, and a protruding portion protruding obliquely rearward and outward from an outer end of the base portion in a widthwise direction of the vehicle seat; and a restriction member provided on the back frame and having a receiving portion capable of supporting a distal end of the protruding portion of the movable member from a rear side thereof, wherein the movable member and the restriction member are adapted, when a rearward load applied to the elastic member is less than a predetermined given value, to be placed in a first mode where the restriction member and the movable member are engaged with each other, and, when the load applied to the elastic member becomes equal to or greater than the given value, to achieve a transition to a second mode where the engagement between the restriction member and the movable member is released, and wherein, in the first mode, a rearward movement of the movable member is restricted by the restriction member, so that the distal end of the protruding portion is supported by the receiving portion and a rearward bending amount of the elastic member is limited, and, in the second mode, the engagement between the movable member and the restriction member is released in such a manner that the protruding portion is moved outward in the widthwise direction of the vehicle seat beyond the receiving portion and the rearward movement of the movable member is permitted, so that the limitation on the bending amount of the elastic member is released.