Seatback and vehicle seat

A seatback configured to support a back of an occupant, the seatback comprising:

• a pressure-receiving member including:
• a first pressure-receiving portion configured to support a lumbar region of the occupant, and
• a second pressure-receiving portion joined to an upper part of the first pressure-receiving portion and configured to support the back of the occupant in cooperation with the first pressure-receiving portion;
• and
• a drive mechanism configured to displace the pressure-receiving member between a support position that is on the occupant's side and a non-support position that is rearward of the support position, and
• a support member that rotatably supports a pressure-receiving plate at a first end thereof in an up-down direction,
• wherein 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,
• wherein the pressure-receiving member comprises the pressure-receiving plate in which the first pressure-receiving portion, the second pressure-receiving portion, and the joining portion are integrated in one piece,
• wherein the joining portion has a lower flexural rigidity than the first pressure-receiving portion and the second pressure-receiving portion and is elastically deformable,
• wherein, when a part of the pressure-receiving plate that is rotatably supported by the support member is referred to as a rotation center, and when a second end, in the up-down direction, of the pressure-receiving plate is referred to as a rotation end, and when a distance from the rotation center to the rotation end is referred to as a pressure-receiving plate length, the rotation end when the pressure-receiving plate is in the support position is located on the occupant's side relative to the rotation end when the pressure-receiving plate is in the non-support position, and
• wherein the pressure-receiving plate length when the pressure-receiving plate is in the support position is smaller than the pressure-receiving plate length when the pressure-receiving plate is in the non-support position.