The present invention relates to an aerosol device formed from: a container containing an aerosol composition comprising one or more propellants and, in an alcoholic or aqueous-alcoholic medium, one or more fixing polymers, and a means for dispensing the said aerosol composition comprising a diffuser equipped with a slit-shaped end orifice that produces a fan-shaped spray. The present invention also relates to a process for treating and especially for shaping keratin fibres, in particular the hair, comprising the use of this device, and to the use of the said device for shaping keratin fibres.
