SEAT

A seat having a seat surface and a backrest includes a support member, a support-member driving unit, a specific-region position estimator, and a controller. The support member is provided in the backrest. The support member is configured to support a predetermined region of a body of a sitter to be seated on the seat and is movable in a vertical direction. The support-member driving unit is configured to drive the support member in the vertical direction relative to the backrest. The specific-region position estimator is configured to estimate a position of a specific region of the sitter that is defined in advance. The controller is configured to control the support-member driving unit such that the support member supports the specific region in accordance with the position of the specific region estimated by the specific-region position estimator.