Abstract: This device for controlling the leaf (5) of a door or window opening to the outside comprises a casing (6) secured to the inner face of the sill (4) of the dormant frame (3) and adapted to house a crank-actuated mechanism for controlling the rotation of an operating arm (7) provided at its end with a roller (13) engaging a guide rail (15) secured to the leaf (5). Protection means (19) are provided for preventing the access to the operating arm (7), notably at the beginning and at the end of the opening and closing movements of the leaf. Locking means (42) are also provided for locking the leaf (5) in any angular position thereof with respect to the dormant frame (3).