in which the pressure applied to the dorsal and lumbar regions of his or her back are substantially equal and in which it is lockable application_number US 80139677 A description let us now refer to fig1 and 6 wherein the numeral 1 denotes the backrest of the seat of the present invention arranged within the backrest 1 is a frame 2 which as can be best seen in fig2 has an inverted 34 u 34 shape and has suspended pendulously therein a frame 3 of a contour varying device generally denoted by 3a as seen in fig1 and 2 a plurality of horizontally strung wires 3a extend tautly between the vertical portions of the frame 3 disposed within the frame 3 are a plurality of fabric tapes 3b which interconnect the wires 3a two hinges 6 or clips adapted to act as hinges are connected to the upper and horizontal portion of the backrest frame 2 to hingedly support the ends of the 34 u 34 shaped frame 3 tension springs 5 extend horizontally between the backrest frame 2 and the frame 3 at locations near the hinges 6 disposed through the backrest frame 2 near the bottom thereof is a crank shaped rod 11 the rod 11 is rotatably supported at its both ends by the backrest frame 2 via means which will be detailed later fixedly connected to the rod 11 are two bars 7 which are arranged to project upwardly in the general direction of the top of the backrest two tension springs 4 are connected between the ends of the two bars and the frame 3 as best seen in fig6 the left hand end of the rod is rotatably.