A headrest storage recession of seat back in an upside-recessed-and-headrest-storage type of seat has, provided at the backward side thereof, an integral combination of a cover element and an upward extension of a back board disposed behind the seat back. Namely, the cover element is connected continuously with the back board upward extension, without any connection line therebetween. A thin hinge portion is defined in boundary between those cover element and upward extension, and the cover element is folded relative to such thin hinge portion and securely attached to the upward extension, thereby constituting a backward wall of the headrest storage recession.