PURPOSE: To save energy and to lessen the wear of an atomizer by selecting the taper angle of the outlet end of a nozzle hole in such a manner that the wear of the nozzle hole by a jet is lessened by lessening the wetting at the front end of the atomizer and that the flow of the jet through the nozzle hole is streamlined. CONSTITUTION: The atomizer 10 consists of a nozzle head 12, the nozzle hole 20, a fluid passage 16 and an air passage 18. The nozzle hole 20 has an inlet end existing at the point proximate to a mixing chamber 24 and the outlet end for ejecting the jet. The atomizer has a minimum diameter portion between the inlet end and the outlet end. The inlet end is gradually tapered inward in a radial direction toward the outlet end and the outlet end is gradually tapered inward in a radial direction toward the inlet end. The taper angle of the outlet end is so selected as to lessen the wear of the nozzle hole 20 by the jet by lessening the wetting at the front end of the atomizer 10 and to streamline the flow of the jet through the nozzle hole 20 in order to reduce the unrestorable pressure drop of the atomizer 10.