SUNSCREEN, comprising a frame which has a passage opening at which a closing wall is placed, which is divided into a lower portion and an upper portion, mutually pivoted by means of a knee and adapted to pass from a stretched configuration, in which said portions (104, 105) are substantially aligned vertically, to a retracted configuration, in which the lower portion is retracted on the upper portion by folding the knee and vice versa; the closing wall also presenting a plurality of louvres capable, when the aforesaid portions (104, 105) are in a stretched configuration, to rotate from a vertical configuration, in which they block the passage of light through the sunscreen, to a horizontal configuration, in which they allow the passage of said light, said sunscreen being characterized in that: - the upper portion comprises two upper primary arms (3, 3'), parallel to and each pivoted at one end thereof on opposite sides of the upper region of the frame and two upper secondary arms (7, 7') parallel to said upper primary arms (3, 3'); in that - the lower portion comprises two lower primary arms (4, 4'), each pivoted at a first end thereof to one of said upper primary arms (3, 3') at the knee, and two lower secondary arms (8, 8'), each pivoted to one of said upper secondary arms (7, 7') at the knee; in that - the louvres extend between the upper and lower secondary arms (7, 7', 8, 8'); in that - at the lateral ends of each louvre a small arm is present, the first end of which is fixed to the louvre and pivoted to the primary arm adjacent thereto, while the remaining end is pivoted on the secondary arm adjacent thereto; in that - the second end of each lower primary arm (4, 4') is pivoted to a primary spool (5, 5') engaged to a lifting belt (13, 13'), which extends vertically along each side of the frame and whose motion is controlled by at least one motor means; and in that - the second end of each lower secondary arm (8, 8') is pivoted to a movable pin (9, 9'), which is placed on the primary spool adjacent thereto and which can move from a lower limit switch to an upper limit switch following the rotation of said primary spool; wherein when each primary spool (5, 5') is blocked with its movable pin (9, 9') at the upper limit switch, the rotation axes of the pins connecting the upper primary and secondary arms to the lower ones are not coincident, while when each primary spool (5, 5') is blocked with its movable pin (9, 9'), at the lower limit switch, the rotation axes of the pins connecting the upper secondary arms to the lower ones are coincident with those of the pins connecting the upper primary arms to the lower ones. - the upper portion comprises two upper primary arms (3, 3'), parallel to and each pivoted at one end thereof on opposite sides of the upper region of the frame and two upper secondary arms (7, 7') parallel to said upper primary arms (3, 3'); in that - the lower portion comprises two lower primary arms (4, 4'), each pivoted at a first end thereof to one of said upper primary arms (3, 3') at the knee, and two lower secondary arms (8, 8'), each pivoted to one of said upper secondary arms (7, 7') at the knee; in that - the louvres extend between the upper and lower secondary arms (7, 7', 8, 8'); in that - at the lateral ends of each louvre a small arm is present, the first end of which is fixed to the louvre and pivoted to the primary arm adjacent thereto, while the remaining end is pivoted on the secondary arm adjacent thereto; in that - the second end of each lower primary arm (4, 4') is pivoted to a primary spool (5, 5') engaged to a lifting belt (13, 13'), which extends vertically along each side of the frame and whose motion is controlled by at least one motor means; and in that - the second end of each lower secondary arm (8, 8') is pivoted to a movable pin (9, 9'), which is placed on the primary spool adjacent thereto and which can move from a lower limit switch to an upper limit switch following the rotation of said primary spool; wherein when each primary spool (5, 5') is blocked with its movable pin (9, 9') at the upper limit switch, the rotation axes of the pins connecting the upper primary and secondary arms to the lower ones are not coincident, while when each primary spool (5, 5') is blocked with its movable pin (9, 9'), at the lower limit switch, the rotation axes of the pins connecting the upper secondary arms to the lower ones are coincident with those of the pins connecting the upper primary arms to the lower ones.