A coating device and method for coating a fiber web for applying coating color onto a fiber web has a nozzle unit with at least one nozzle part (10), a feeding chamber (11) and at least one equalizing chamber (13; 13′), a feed hole (12) between the feeding chamber (11) and the first equalizing chamber (13), and a nozzle slot (14′) from which the coating color is discharged through the nozzle slot (14′) outlet opening (15). A mixing chamber (20) between the outlet area of the feed hole (12) and the equalizing chamber (13) functions as a means for distributing uniformly the inhomogeneous coating color flow entering the equalizing chamber (13) from the feed hole (12). The coating from the feed hole is directed to a wall (22) of mixing chambers (20) which distribute uniformly the coating entering the equalizing chamber (13).