Turbofan having a longitudinal direction and comprising a motor and a nacelle, surrounding the motor, which comprises a fan casing, in which a duct for a bypass flow is delimited between the nacelle and the motor and in which a flow of air flows in a flow direction, said nacelle comprising: - a fixed structure fixed to the fan casing and comprising a guide vanes support bearing guide vanes, - a mobile cowl able to move in translation, on the fixed structure, in a direction of translation between an advanced position in which the mobile cowl is positioned such that it is moved close to the fan casing and a retracted position in which the mobile cowl is positioned such that it is moved away from the fan casing so as to define, between them, an open window between the duct and the exterior of the nacelle, and facing the guide vanes, - a plurality of arms, each one comprising a distal end and a proximal end which is mounted so as to be mobile in rotation on the guide vanes support about an axis of rotation parallel overall to the longitudinal direction, wherein each arm is mobile between a stowed position in which the arm is outside the duct and a deployed position in which the arm is across the duct, - for each pair of adjacent arms, a flexible screen extending angularly between the two arms and adopting the form of a portion of an annulus with an exterior edge having a large radius and an interior edge having a small radius, wherein the exterior edge is attached to the guide vanes support rearward of the guide vanes, and wherein the distal end of each arm of the pair is fixed along the interior edge of the flexible screen, - for each pair of arms, a link rod of which one end is mounted articulated to the distal end of one of the arms of the pair and the other end is mounted articulated to the distal end of the other arm of the same pair, - a set of actuators causing the mobile cowl to move between the advanced position and the retracted position, and vice versa, and - an operating system intended to move each arm from the stowed position to the deployed position when the mobile cowl passes from the advanced position to the retracted position, and to move each arm from the deployed position to the stowed position when the mobile cowl passes from the retracted position to the advanced position. - a fixed structure fixed to the fan casing and comprising a guide vanes support bearing guide vanes, - a mobile cowl able to move in translation, on the fixed structure, in a direction of translation between an advanced position in which the mobile cowl is positioned such that it is moved close to the fan casing and a retracted position in which the mobile cowl is positioned such that it is moved away from the fan casing so as to define, between them, an open window between the duct and the exterior of the nacelle, and facing the guide vanes, - a plurality of arms, each one comprising a distal end and a proximal end which is mounted so as to be mobile in rotation on the guide vanes support about an axis of rotation parallel overall to the longitudinal direction, wherein each arm is mobile between a stowed position in which the arm is outside the duct and a deployed position in which the arm is across the duct, - for each pair of adjacent arms, a flexible screen extending angularly between the two arms and adopting the form of a portion of an annulus with an exterior edge having a large radius and an interior edge having a small radius, wherein the exterior edge is attached to the guide vanes support rearward of the guide vanes, and wherein the distal end of each arm of the pair is fixed along the interior edge of the flexible screen, - for each pair of arms, a link rod of which one end is mounted articulated to the distal end of one of the arms of the pair and the other end is mounted articulated to the distal end of the other arm of the same pair, - a set of actuators causing the mobile cowl to move between the advanced position and the retracted position, and vice versa, and - an operating system intended to move each arm from the stowed position to the deployed position when the mobile cowl passes from the advanced position to the retracted position, and to move each arm from the deployed position to the stowed position when the mobile cowl passes from the retracted position to the advanced position.