An extensible cord lead comprising a casing (11) containing a winding wheel (13) equipped with housings (15) intercepted by a pushbutton (16) to allow the partial or total blocking of the cord, the pushbutton (16) being equipped with a forward position blocking device consisting of a cursor (20) which slides or rotates in a transverse direction with respect to the axis of the pushbutton (16) in which it is inserted, said cursor (20) being activated by a thumb-turn (21) located on the head of the pushbutton (16), said cursor (20) being able to move from a blocked position to free sliding of the pushbutton, entering and exiting transversally to the sliding axis of the pushbutton (16), in a housing (22) in the box-like casing (11) of the winding device.
