Abstract: Provided is a chair which comprises a lumbar support that is capable of comfortably supporting the lumbar region and that is capable of providing stable support with a side frame pole of a back frame. This invention comprises: a lumbar support main body (41) in which a lumbar support (10) that is provided on the chair has a top-to-bottom dimension that gradually becomes smaller from the left and right ends toward the center by having the lower edge of the center in the left/right direction curving upward in an arc shape; four attaching portions (42) which are provided on both sides of the lumbar support main body (41) so as to be separated in the vertical direction and which are movably supported in the vertical direction by guide portions that are provided on the left and right side frame poles (19) and that are directed vertically; and operating members (44) which are linked with the left and right lower attaching portions (42).