A device (D) for adjusting ventilation on board of vehicles, the device comprising at least one control unit (C) connectable to at least one command element (E) of a ventilation system on a vehicle and to at least one ventilation device (V) of said system, said control unit (C) having generation means for generating an output current (I out ) for supplying said ventilation device (V) according to at least one input signal (S in ) coming from said command element (E), the device characterized by that the device comprises at least one adjustment unit (S) connected to said control unit (C) and configured for adjusting said output current (I out ) according to the minimum current required to supply said ventilation device (V) and to the maximum current absorbable by said ventilation device (V), wherein said adjustment unit (S) comprises: - a generation power circuit (S2) for generating a reference current (I ref ); - a correction power circuit (S1) connected to said generation power circuit (S2) and comprising at least two branches (B1, B2, B3, B4) normally open and arranged in parallel to each other, wherein each of said branches (B1, B2, B3, B4) has an electric resistor (R1, R2, R3, R4) of different values the one from the other and closing means (P1, P2, P3, P4) of the branch (B1, B2, B3, B4), wherein at least one of said branches (B1, B2, B3, B4) is configured to be closed through said closing means (P1, P2, P3, P4) for varying said reference current (I ref ) according to the minimum current required to supply said ventilation device (V) and to the maximum current absorbable by said ventilation device; - a comparison power circuit (S3) for comparing said output current (I out ) and said reference current (I ref ), connected to said generation power circuit (S2) of the reference current (I ref ) and to said control unit (C), wherein said comparison power circuit (S3) comprises means for varying said output current (I out ) according to said difference found between said output current (I out ) and said reference current (I ref ). - a generation power circuit (S2) for generating a reference current (I ref ); - a correction power circuit (S1) connected to said generation power circuit (S2) and comprising at least two branches (B1, B2, B3, B4) normally open and arranged in parallel to each other, wherein each of said branches (B1, B2, B3, B4) has an electric resistor (R1, R2, R3, R4) of different values the one from the other and closing means (P1, P2, P3, P4) of the branch (B1, B2, B3, B4), wherein at least one of said branches (B1, B2, B3, B4) is configured to be closed through said closing means (P1, P2, P3, P4) for varying said reference current (I ref ) according to the minimum current required to supply said ventilation device (V) and to the maximum current absorbable by said ventilation device; - a comparison power circuit (S3) for comparing said output current (I out ) and said reference current (I ref ), connected to said generation power circuit (S2) of the reference current (I ref ) and to said control unit (C), wherein said comparison power circuit (S3) comprises means for varying said output current (I out ) according to said difference found between said output current (I out ) and said reference current (I ref ). <EOS>