Abstract: A fuel injector including a valve housing having a nozzle for columnarly injecting fuel and a valve seat continuing from the nozzle; a valve body reciprocatably mounted in the valve housing and having a valve portion adapted to abut against and retract from the valve seat and thereby close and open the nozzle, respectively; and an adapter fixed to a front end of the valve housing. The adapter is formed with an atomizer hole communicating with the nozzle and an assist air passage extending through a side wall of the adapter for supplying an assist air into the atomizer hole to atomize the columnar fuel injected from the nozzle. Both the valve portion and the valve seat are formed to have surfaces in a conical shape so that upon retraction of the valve portion, the space generated between the surfaces becomes uniform over substantially the length of the surfaces.