A connecting device (1) for connecting therebetween the respective ends of two ducts prevents that the inside portion of the ducts comes in contact with the atmosphere and with polluting agents before the complete connection thereof by keeping the connection procedure simple to be performed and it comprises two connecting members (2, 4) provided with tubular ends (12, 27) and respective concentric and coaxial tubular casings (17, 32), which penetrate by breaking in sequence respective breakable barriers (20, 40) arranged inside said connection members (2, 4), wherein at lest one of said first and second connecting member (2, 4) comprises a sliding guide comprising at least a groove formed on a surface of an outer cylindrical casing (6) of a connecting member (2), apt to cooperate with a corresponding rib or with one or more teeth (9) implemented at an inner surface of an outer cylindrical casing (8) of the other connecting member (4).
