A method and a device reduces the vibration generated on the structure 17 of a helicopter 2 by the flow of air through the main rotor 5 and by the flow of air along the fuselage 3. The device 1 includes: at least one sensor 18, 19, 20 measuring the vibration generated on the structure 17; and computer element 30 responsive to the vibration measurements to determine variation in the angle of incidence of a tail fin 9 of the helicopter 2 suitable for generating an opposing force {right arrow over (T1)}, {right arrow over (T2)} for opposing the vibration, and transmitting the variation in angle of incidence as determined in this way to a control system 10 for controlling the angle of incidence of the tail fin 9.