SEAT STRUCTURE

A seat back includes: a top-surface seat cover disposed on the top surface; a top-surface cushion pad arranged on a back side of the top-surface seat cover; a contact-surface seat cover disposed on the contact surface; a contact-surface cushion pad arranged on a back side of the contact-surface seat cover and under the top-surface cushion pad; and an airbag having adjustable internal air volume, wherein a lower end portion of the top-surface seat cover is fixed to a first anchorage within the seat back, while covering a lower surface of the top-surface cushion pad, and an upper end portion of the contact-surface seat cover is fixed to a second anchorage within the seat back, while covering an upper surface of the contact-surface cushion pad.