Abstract: A connecting device includes a first body (1) and a second body (2) which are automatically lockingly engageably with one another. Elastic tongues (6) with stop dogs (7) are associated with the second body (2), and a groove (4) on the first body (1) is engaged by the stop dogs (7). A chuck (16) with a frustoconical cam (25) maintains the stop dogs (7) in the groove (4) and connects axially by a resilient split washer (19) to the second body (2). A manual unlocking ring (27) is mounted for axial movement on the chuck (16) to release the stop dogs (7) from the groove (4). A nut (29) engaged on a thread (28) of the first body (1) makes it possible to block the stop dogs (7) in the groove (4) and to immobilize the unlocking ring (27) by clamping against the chuck (16), so as to prevent any unintentional, accidental or improper unlocking.