Seatback and vehicle seat

A seatback includes a pressure-receiving member and a drive mechanism. The pressure-receiving member includes a first pressure-receiving portion configured to support a lumbar region of an occupant, and a second pressure-receiving portion joined to an upper part of the first pressure-receiving portion and configured to support a back of the occupant in cooperation with the first pressure-receiving portion. The drive mechanism is configured to displace the pressure-receiving member between a support position and a non-support position, which is a position rearward of the support position. The pressure-receiving member is configured, when in the support position, to be bent at a joining portion where the first pressure-receiving portion and the second pressure-receiving portion are joined together to become convex toward a seat front side.