A device for constraining the opening of doors or windows comprising a fixed frame, a movable frame or leaf, a control handle associated with the leaf; the handle being connected to devices for locking/unlocking the leaf slidably positioned along the perimeter profile of the leaf to allow, by rotating the handle, at least a closed configuration of the leaf and a configuration for free opening of the leaf, the constraining device comprising: - a guide body associated with the perimeter profile of the movable leaf and having a slot; - an operating arm articulated, at a first end, to the fixed frame, and a second end slidably connectable, by a pin, inside the slot of the guide body so as to allow a sliding stroke of the pin along the guide slot to define an open configuration with a limited angle of the leaf; characterised in that it comprises: - the guide body provided with two lateral openings facing each other made on the walls defining the slot to allow a free passage, at least through one of the openings, of the pin of the arm housed in the slot when the leaf is in the free open configuration; - a locking lever or latch articulated to a base of the guide body and movable between a first, lowered non-operating position and a second, raised operating position for locking the pin of the arm when it is positioned at an end of the slot of the guide body in the open configuration with a limited angle of the leaf; - an operating rod slidably inserted along the guide body and having its ends, outside the guide body, configured to connect, in use, with the devices for locking / unlocking the movable leaf; said rod having a pair of protruding walls configured to temporarily close, in use, the openings of the slot at least at the passage from the closed configuration to the open configuration with a limited angle of the leaf. - a guide body associated with the perimeter profile of the movable leaf and having a slot; - an operating arm articulated, at a first end, to the fixed frame, and a second end slidably connectable, by a pin, inside the slot of the guide body so as to allow a sliding stroke of the pin along the guide slot to define an open configuration with a limited angle of the leaf; characterised in that it comprises: - the guide body provided with two lateral openings facing each other made on the walls defining the slot to allow a free passage, at least through one of the openings, of the pin of the arm housed in the slot when the leaf is in the free open configuration; - a locking lever or latch articulated to a base of the guide body and movable between a first, lowered non-operating position and a second, raised operating position for locking the pin of the arm when it is positioned at an end of the slot of the guide body in the open configuration with a limited angle of the leaf; - an operating rod slidably inserted along the guide body and having its ends, outside the guide body, configured to connect, in use, with the devices for locking / unlocking the movable leaf; said rod having a pair of protruding walls configured to temporarily close, in use, the openings of the slot at least at the passage from the closed configuration to the open configuration with a limited angle of the leaf. - the guide body provided with two lateral openings facing each other made on the walls defining the slot to allow a free passage, at least through one of the openings, of the pin of the arm housed in the slot when the leaf is in the free open configuration; - a locking lever or latch articulated to a base of the guide body and movable between a first, lowered non-operating position and a second, raised operating position for locking the pin of the arm when it is positioned at an end of the slot of the guide body in the open configuration with a limited angle of the leaf; - an operating rod slidably inserted along the guide body and having its ends, outside the guide body, configured to connect, in use, with the devices for locking / unlocking the movable leaf; said rod having a pair of protruding walls configured to temporarily close, in use, the openings of the slot at least at the passage from the closed configuration to the open configuration with a limited angle of the leaf.