Seatback of vehicle seat

A seatback of a vehicle seat, the seatback comprising:

• a cushion member including a seat width direction central section, and a pair of side sections respectively connected to a pair of side edge portions of the central section so as to be rotatable relative to the central section about the side edge portions;
• a lumbar support configured to contact a rear face of the central section and to be deformable such that a front-rear direction position of part of the lumbar support is changed;
• a covering member having a bag shape and covering the cushion member and the lumbar support;
• a pair of side restraint members configured so as to be connected to an inner face of the covering member and to respectively restrain the pair of side sections;
• and
• a pair of back face restraint members provided at an inner face of a back face configuration section of the covering member and, by being respectively connected to the pair of side restraint members, configured to cause the back face configuration section to approach closer to the lumbar support than would be the case were they not to be connected to the side restraint members.