A vehicle seat comprising: a seat back; and a back frame provided inside the seat back to support the headrest, the back frame including: right and left side frames (12, 12), and a support spring unit (20B, 20C) having opposite right and left ends (20b, 20c) locked between the right and left side frames (12, 12) and extending in a right-left direction to support a lumber region of an occupant, wherein the support spring unit (20B, 20C) is shaped such that a central region thereof protrudes frontwardly relative to the right and left ends thereof in an approximately flat state, wherein the support spring unit comprises a plurality of support spring members (20B, 20C) arranged between the right and left side frames (12, 12) in mutually spaced-apart relation in an up-down direction, and wherein the vehicle seat includes a coupling member (15, 15) provided on right and left sides of the vehicle seat to couple the plurality of support spring members (20B, 20C) together, and characterized in that said vehicle seat further comprises a headrest; and a return spring member having one end locked to one of the right and left side frames (12, 12) and the other end locked to the support spring unit (20B, 20C), wherein the return spring member being adapted, when the frontwardly protruding central region of the support spring unit (20B, 20C) is depressed rearwardly due to a rearward load applied thereto, to bias the central region of the support spring unit (20B, 20C) in a direction for causing it to return to the frontwardly protruding shape, and wherein the return spring member is provided on right and left sides of the vehicle seat, the one end and the other end of each of the return spring members (22, 22) being locked to a corresponding one of the right and left side frames (12, 12) and a corresponding one of the right and left coupling members (15, 15), respectively. a seat back; and a back frame provided inside the seat back to support the headrest, the back frame including: right and left side frames (12, 12), and a support spring unit (20B, 20C) having opposite right and left ends (20b, 20c) locked between the right and left side frames (12, 12) and extending in a right-left direction to support a lumber region of an occupant, wherein the support spring unit (20B, 20C) is shaped such that a central region thereof protrudes frontwardly relative to the right and left ends thereof in an approximately flat state, wherein the support spring unit comprises a plurality of support spring members (20B, 20C) arranged between the right and left side frames (12, 12) in mutually spaced-apart relation in an up-down direction, and wherein the vehicle seat includes a coupling member (15, 15) provided on right and left sides of the vehicle seat to couple the plurality of support spring members (20B, 20C) together, and right and left side frames (12, 12), and a support spring unit (20B, 20C) having opposite right and left ends (20b, 20c) locked between the right and left side frames (12, 12) and extending in a right-left direction to support a lumber region of an occupant, wherein the support spring unit (20B, 20C) is shaped such that a central region thereof protrudes frontwardly relative to the right and left ends thereof in an approximately flat state, wherein the support spring unit comprises a plurality of support spring members (20B, 20C) arranged between the right and left side frames (12, 12) in mutually spaced-apart relation in an up-down direction, and wherein the vehicle seat includes a coupling member (15, 15) provided on right and left sides of the vehicle seat to couple the plurality of support spring members (20B, 20C) together, and a headrest; and a return spring member having one end locked to one of the right and left side frames (12, 12) and the other end locked to the support spring unit (20B, 20C), wherein the return spring member being adapted, when the frontwardly protruding central region of the support spring unit (20B, 20C) is depressed rearwardly due to a rearward load applied thereto, to bias the central region of the support spring unit (20B, 20C) in a direction for causing it to return to the frontwardly protruding shape, and wherein the return spring member is provided on right and left sides of the vehicle seat, the one end and the other end of each of the return spring members (22, 22) being locked to a corresponding one of the right and left side frames (12, 12) and a corresponding one of the right and left coupling members (15, 15), respectively.