A seat back configured to support a back of a seated person includes a back frame constituting an internal framework; and an elastic mat fitted to the back frame so as to cover the back frame from a front side, the elastic mat having a planar shape and being configured to elastically support the back of the seated person. The back frame includes a frame body and a support wire that protrudes forward from the frame body. The elastic mat includes a main support portion configured to support the back of the seated person, and a band portion that extends from a back surface of the main support portion, the band portion being wound around the support wire. The elastic mat has a through-hole through which a head at a distal end of the wound band portion is inserted such that the head is snap-fitted in the through-hole.