Device for the towing vehicle-trailer connection, characterized in that it comprises: - a base body associable with a trailer and wherein is defined at least a first female coupling, communicating with a control line of the braking system of the trailer, and at least a second female coupling, communicating with at least an additional line which acts on the parking and/or automatic brake of the trailer and with at least a by-pass line communicating with an unloading tank; - at least a first and a second male couplings (12, 13) associated with a towing vehicle of the trailer and connectable to the relative braking system, where said first and second male couplings (12, 13) can be connected to valves able to send to the same, respectively, a working fluid at a first and at a second pressure and are insertable, respectively, within said first and second female couplings (3, 6); valve means being provided able to be put in communication and isolate between them said additional line with said by-pass line, respectively, as a result of the exit and insertion of said male couplings (12, 13) from the relative female couplings (3, 6); - at least a connection element which has at least a first ring nut fitted around said first female coupling and at least a second ring nut fitted around said second female coupling, said first and the second ring nuts (18a, 18b) being locked together, said connection element being associated movable with respect to said base body between a release position, wherein it allows the displacement of said male couplings (12, 13) with respect to the relative female couplings (3, 6), and a fastening position, wherein it prevents the displacement of said male couplings (12, 13) with respect to the relative female couplings (3, 6); - fastening and release means able to cooperate with one another to allow the locking and unlocking of said male couplings (12, 13) with respect to said female couplings (3, 6) as a result of the achievement by said connection element of said fastening position and of said release position, respectively. - a base body associable with a trailer and wherein is defined at least a first female coupling, communicating with a control line of the braking system of the trailer, and at least a second female coupling, communicating with at least an additional line which acts on the parking and/or automatic brake of the trailer and with at least a by-pass line communicating with an unloading tank; - at least a first and a second male couplings (12, 13) associated with a towing vehicle of the trailer and connectable to the relative braking system, where said first and second male couplings (12, 13) can be connected to valves able to send to the same, respectively, a working fluid at a first and at a second pressure and are insertable, respectively, within said first and second female couplings (3, 6); valve means being provided able to be put in communication and isolate between them said additional line with said by-pass line, respectively, as a result of the exit and insertion of said male couplings (12, 13) from the relative female couplings (3, 6); - at least a connection element which has at least a first ring nut fitted around said first female coupling and at least a second ring nut fitted around said second female coupling, said first and the second ring nuts (18a, 18b) being locked together, said connection element being associated movable with respect to said base body between a release position, wherein it allows the displacement of said male couplings (12, 13) with respect to the relative female couplings (3, 6), and a fastening position, wherein it prevents the displacement of said male couplings (12, 13) with respect to the relative female couplings (3, 6); - fastening and release means able to cooperate with one another to allow the locking and unlocking of said male couplings (12, 13) with respect to said female couplings (3, 6) as a result of the achievement by said connection element of said fastening position and of said release position, respectively.