A lumbar support apparatus includes a curved plate which is provided to a seat-back frame so that the upper part of the curved plate is rotatable in the vertical direction, and which is deformable in the direction in which a seated person's lumbar spine is pressed; a curved-plate deformation-amount adjustment unit including a threaded rod having an external thread formed on the peripheral surface thereof, and a nut member that is threadedly engaged with the external thread of the threaded rod and is attached to the lower part of the curved plate so as to be prohibited from rotating about a center axis and so as to be movable in the vertical direction; and a drive unit for rotatingly driving the threaded rod.