A lumbar support structure arranged in a seat back, the lumbar support structure being installed in a back-surface side of a back cushioning member having a tensile structure bridgeable in a back frame composing the seat back, and comprising: a lower lumbar support that has a first torsion bar and a first support plate that is supported by the first torsion bar and can be displaced elastically by receiving a load, the first support plate being set in a lower portion of the back frame, the lower lumbar support supporting elastically the back cushioning member and imparting a restoring force; and an upper lumbar support that has a second torsion bar, a second support plate that is supported by the second torsion bar and can be displaced elastically by receiving a load, and a lumbar adjustment means that twists the second torsion bar and adjusts a position of the second support plate to front and back, the second support plate being set in an upper portion of the first support plate, wherein the first support plate of the lower lumbar support is set in a position corresponding to a pelvic part of a seated person, and the second support plate of the upper lumbar support is set in a position corresponding to a lumbar part of the seated person characterized in that an upper side portion of the first torsion bar is connected to near an upper edge portion of the first support plate, each of end portions of the first torsion bar is connectable to an engaging portion provided near the rearward in a side view, in a lower portion of the back frame and the first torsion bar is set so that the upper side portion is energized forward having each of the end portions as a center. the lumbar support structure being installed in a back-surface side of a back cushioning member having a tensile structure bridgeable in a back frame composing the seat back, and comprising: a lower lumbar support that has a first torsion bar and a first support plate that is supported by the first torsion bar and can be displaced elastically by receiving a load, the first support plate being set in a lower portion of the back frame, the lower lumbar support supporting elastically the back cushioning member and imparting a restoring force; and an upper lumbar support that has a second torsion bar, a second support plate that is supported by the second torsion bar and can be displaced elastically by receiving a load, and a lumbar adjustment means that twists the second torsion bar and adjusts a position of the second support plate to front and back, the second support plate being set in an upper portion of the first support plate, wherein the first support plate of the lower lumbar support is set in a position corresponding to a pelvic part of a seated person, and the second support plate of the upper lumbar support is set in a position corresponding to a lumbar part of the seated person characterized in that an upper side portion of the first torsion bar is connected to near an upper edge portion of the first support plate, each of end portions of the first torsion bar is connectable to an engaging portion provided near the rearward in a side view, in a lower portion of the back frame and the first torsion bar is set so that the upper side portion is energized forward having each of the end portions as a center.