A corner and safety transmission assembly for an actuating linkage of a metallic window or door frame with wing and swivel opening, which includes an “L” shaped guiding body able to be fastened on the exterior of an upper corner of the movable frame of the window or door; a first and a second slidable member, mounted slidable on respective branches of the guiding body; a flexible element that interconnects said slidable members; and a safety block including a body in which is mounted a bolt able to slide transversely relative to the direction of motion of the first slidable member and against the action of elastic means. The guiding body has two transverse guides between which is inserted the body of the safety block. The first slidable member has two segments with different heights and the body of the safety block has on one side oriented towards the guiding body an opening directed in the longitudinal direction engageable by the segment with greater height of the slidable member to prevent a motion in the transverse direction of the body of the safety block.