A gas safety valve (1) capable of avoiding unwanted or inadvertent opening and possible closing, with maximum safety and allowing an opening, and possible closing, of these safety valves only through a double intentional and reliable maneuver includes a knob (22) for controlling the shutter (7) of the valve (1), during the opening and closing rotation movement, stop projections (32, 33) of the valve (1) slide on sliding segments (37, 38; 37B, 38B) provided in the knob (22) coplanar or flat-like inclined and associated to relative positioning projections (41, 42), a spring (28) housed in a chamber between a threaded end (19) of a screw (11), and a chamber (23) of the knob (22).