Roller blind, which comprises: - a support frame intended to be fixed to a load-bearing element; - a take-up roller rotatably constrained to said support frame and having a rotation axis; - two lateral guides extended parallel to each other and side-by-side along respective first extension directions substantially orthogonal to the rotation axis of said take-up roller; each said lateral guide extended along the corresponding said first extension direction between a first end, positioned at said take-up roller, and an opposite second end; each said lateral guide being provided with an external surface which comprises: - a first lateral side directed towards the first lateral side of the other said lateral guide, and on such first lateral side a longitudinal opening is made that is parallel to said first extension direction, - a second lateral side directed in a direction substantially opposite said first lateral side, - a frontal face extended to connect said first lateral side with said second lateral side; - a fabric extended between a first edge thereof fixed to said take-up roller and a second edge thereof, and susceptible of sliding between said lateral guides; - a transverse bar fixed to the second edge of said fabric and extended, along a second extension direction parallel to the rotation axis of said take-up roller, between two lateral ends thereof slidably engaged in the longitudinal openings of the corresponding said lateral guides; said transverse bar being movable between an open position, in which said transverse bar is placed at the first ends of said lateral guides, and a closed position, in which said transverse bar is positioned at the second ends of said lateral guides; said blind also comprising: - at least one first magnetic coupling element fixed to the corresponding said lateral guide; - at least one second magnetic coupling element, which is fixed to said transverse bar and is provided with a lateral appendage, which is projectingly extended in front of the frontal face of the external surface of the corresponding said lateral guide and, with said transverse bar arranged at least in said closed position, is engaged via magnetic attraction to said first magnetic coupling element in order to retain said transverse bar in said closed position. - a support frame intended to be fixed to a load-bearing element; - a take-up roller rotatably constrained to said support frame and having a rotation axis; - two lateral guides extended parallel to each other and side-by-side along respective first extension directions substantially orthogonal to the rotation axis of said take-up roller; each said lateral guide extended along the corresponding said first extension direction between a first end, positioned at said take-up roller, and an opposite second end; each said lateral guide being provided with an external surface which comprises: - a first lateral side directed towards the first lateral side of the other said lateral guide, and on such first lateral side a longitudinal opening is made that is parallel to said first extension direction, - a second lateral side directed in a direction substantially opposite said first lateral side, - a frontal face extended to connect said first lateral side with said second lateral side; - a first lateral side directed towards the first lateral side of the other said lateral guide, and on such first lateral side a longitudinal opening is made that is parallel to said first extension direction, - a second lateral side directed in a direction substantially opposite said first lateral side, - a frontal face extended to connect said first lateral side with said second lateral side; - a fabric extended between a first edge thereof fixed to said take-up roller and a second edge thereof, and susceptible of sliding between said lateral guides; - a transverse bar fixed to the second edge of said fabric and extended, along a second extension direction parallel to the rotation axis of said take-up roller, between two lateral ends thereof slidably engaged in the longitudinal openings of the corresponding said lateral guides; said transverse bar being movable between an open position, in which said transverse bar is placed at the first ends of said lateral guides, and a closed position, in which said transverse bar is positioned at the second ends of said lateral guides; said blind also comprising: - at least one first magnetic coupling element fixed to the corresponding said lateral guide; - at least one second magnetic coupling element, which is fixed to said transverse bar and is provided with a lateral appendage, which is projectingly extended in front of the frontal face of the external surface of the corresponding said lateral guide and, with said transverse bar arranged at least in said closed position, is engaged via magnetic attraction to said first magnetic coupling element in order to retain said transverse bar in said closed position. - at least one first magnetic coupling element fixed to the corresponding said lateral guide; - at least one second magnetic coupling element, which is fixed to said transverse bar and is provided with a lateral appendage, which is projectingly extended in front of the frontal face of the external surface of the corresponding said lateral guide and, with said transverse bar arranged at least in said closed position, is engaged via magnetic attraction to said first magnetic coupling element in order to retain said transverse bar in said closed position.