An automatically retractable pet leash, comprises a casing or guard (10)inside which is a winding device of a cord orribbon that protrudes from the casing or guard (10) through an aperture (13),and a braking mechanism operated by a pushbutton(12), and also comprises a handle (11) for gripping the leash with one hand.It also comprises a protective shell (14) designed to protectthe casing or guard (10) from knocks or blows that can damage it； the casingor guard comprises at least one housing designed toaccommodate by snap-fitting, when used, at least one coupling or ribbingelement foreseen on the body of the protective shell (14) insuch a way as to hold the protective shell (14) locked against the casing orguard (10).
