The coupling device for ducts comprises locking elements (12, 55) constrained to the flange (11, 41) of a first duct (10, 40) which are connected to movement means (18, 47) to move them toward or away from the flange (30, 31, 32) of a second duct (80, 81). The movement means (18, 47) are actuated by a thrust ring (17, 50) which is rotated around the axis of the first duct (10, 40). Along the contact side of the flange (11, 41) of the first duct (10, 40) are provided elastically stressed seals (16) which interact between the flange (11, 41) of the first duct and the flange (30, 31, 32) of said connected duct. Said seals (16) consist of floating rings running and oscillating in recesses (14) made in the flange (11, 41), said floating rings being acted upon by elastic elements (13) inserted in said recesses (14).