A sliding door wing supporting device, for closing and opening an aperture, defining a sliding direction of the supporting device, and comprising: a fixing plate (10, 10', 10"), adapted to be fixed to a structure in which the aperture is present, forming a first member of a first kinematic sliding pair, defining a first length, an intermediate rail (11, 11', 11"), arranged by a side of the fixing plate (10, 10',10"), forming a second member of the first kinematic sliding pair and also forming a first member of a second kinematic sliding pair, defining a second length, an outer rail (12, 12', 12") for fixing a wing of said sliding door, arranged by the side of the intermediate rail (11, 11', 11 ") and forming a second member of the second kinematic sliding pair, wherein the outer rail (12, 12', 12") has a length substantially equal to the second length in the way of the sliding direction, wherein the supporting device can slide between two extreme positions, a retracted position in which the fixing plate (10, 10', 10"), the intermediate rail (11, 11', 11"), the outer rail (12, 12', 12") have a respective first aligned end, and a position of maximum extension in which the intermediate rail (11, 11', 11") protrubes beyond the fixing plate (10, 10', 10") by a segment X, and the outer rail (12, 12', 12") protrubes beyond the intermediate rail (11, 11', 11") by a segment V, so as to leave only a segment of intermediate rail (11, 11', 11") not covered by the outer rail (12, 12', 12") wherein the first kinematic sliding pair allows the intermediate rail (11, 11', 11 ") to slide with respect to the fixing plate (10, 10', 10") along said sliding direction through first sliding means, and the second kinematic sliding pair allows the outer rail (12, 12', 12") to slide with respect to the intermediate rail (11, 11 ', 11 ") along said sliding direction through second sliding means, wherein the second sliding means are arranged only in surface portion of the intermediate rail (11, 11', 11") which always remains covered by the outer rail (12, 12', 12"), characterised in that the first length is smaller than the second length, and in that the first sliding means (13, 14, 40, 41) are arranged on the fixing plate (10, 10', 10") so that during sliding between the two extreme positions the fixing plate (10, 10', 10") does not protrude from the ends of the intermediate rail (11, 11', 11 "). a fixing plate (10, 10', 10"), adapted to be fixed to a structure in which the aperture is present, forming a first member of a first kinematic sliding pair, defining a first length, an intermediate rail (11, 11', 11"), arranged by a side of the fixing plate (10, 10',10"), forming a second member of the first kinematic sliding pair and also forming a first member of a second kinematic sliding pair, defining a second length, an outer rail (12, 12', 12") for fixing a wing of said sliding door, arranged by the side of the intermediate rail (11, 11', 11 ") and forming a second member of the second kinematic sliding pair, wherein the outer rail (12, 12', 12") has a length substantially equal to the second length in the way of the sliding direction, wherein the supporting device can slide between two extreme positions, a retracted position in which the fixing plate (10, 10', 10"), the intermediate rail (11, 11', 11"), the outer rail (12, 12', 12") have a respective first aligned end, and a position of maximum extension in which the intermediate rail (11, 11', 11") protrubes beyond the fixing plate (10, 10', 10") by a segment X, and the outer rail (12, 12', 12") protrubes beyond the intermediate rail (11, 11', 11") by a segment V, so as to leave only a segment of intermediate rail (11, 11', 11") not covered by the outer rail (12, 12', 12") wherein the first kinematic sliding pair allows the intermediate rail (11, 11', 11 ") to slide with respect to the fixing plate (10, 10', 10") along said sliding direction through first sliding means, and the second kinematic sliding pair allows the outer rail (12, 12', 12") to slide with respect to the intermediate rail (11, 11 ', 11 ") along said sliding direction through second sliding means, wherein the second sliding means are arranged only in surface portion of the intermediate rail (11, 11', 11") which always remains covered by the outer rail (12, 12', 12"), characterised in that the first length is smaller than the second length, and in that the first sliding means (13, 14, 40, 41) are arranged on the fixing plate (10, 10', 10") so that during sliding between the two extreme positions the fixing plate (10, 10', 10") does not protrude from the ends of the intermediate rail (11, 11', 11 ").