The invention relates to a motor vehicle seat back structure comprising a backrest support frame which consists of a surface turned towards the seat user's back, a lordosis support which is arranged on the front part of the backrest support frame for supporting the user's back and an adjusting device for vertically adjusting the lordosis support position with respect to the extension plane of said backrest support frame. Said invention is characterised in that the adjusting device comprises at least one adjusting element (11, 12) operably connected to the lordosis support and at least one sliding element (21, 22) which is displaceable with respect to said adjusting element (11, 12) and interacts therewith in such a way that when the sliding element (21, 22) moves, the adjusting element (11, 12) is displaced with a directional component (x) perpendicularly to the displacement direction (y, z) of the sliding element (21, 22) and performs an action on said lordosis support in the direction (x).