NOVELTY - A raw-material-oil fat and lower alcohol are mixed and supplied to a catalytic reaction pipe in a reactor (100) to obtain fatty acid ester and glycerin. The effluent from catalytic reaction pipe is introduced into a glycerin separation tank (40) to recover glycerin. A lower alcohol is added to a supernatant liquid from which glycerin is separated, mixed and supplied to the other catalytic reaction pipe. The effluent from the catalytic reaction pipe of last stage is introduced into the glycerin separation tank. The fatty acid ester is recovered from the supernatant liquid.    USE - Continuous production of fatty acid ester used as biodiesel fuel for motor vehicle.    ADVANTAGE - The method enables continuous production of fatty acid ester efficiently and economically, without washing process. The concentration of lower alcohol is controlled efficiently and the glycerin byproduct is removed easily. The biodiesel fuel formed using the fatty acid ester is eco-friendly.    DETAILED DESCRIPTION - A raw-material-oil fat and lower alcohol are mixed and supplied to a catalytic reaction pipe in a reactor comprising catalytic reaction pipes filled with lipase to obtain fatty acid ester and glycerin. The effluent from the catalytic reaction pipe is introduced into a glycerin separation tank to recover glycerin. A lower alcohol is added to a supernatant liquid from which glycerin is separated, mixed and supplied to the other catalytic reaction pipe. The generation of fatty acid ester and glycerin, introduction of effluent from the catalytic reaction pipe to glycerin separation tank and addition of lower alcohol to supernatant liquid are repeated. The effluent from the catalytic reaction pipe of last stage is introduced into the glycerin separation tank which is provided downstream from the catalytic reaction pipe of last stage to recover glycerin, and to obtain supernatant liquid. The fatty acid ester is recovered from the supernatant liquid. An INDEPENDENT CLAIM is included for apparatus for producing fatty acid ester, which has multi-staged catalytic reaction pipe (10) filled with lipase, a glycerin separation tank provided downstream from a catalytic reaction pipe, and separates effluent from the catalytic reaction pipe into glycerin and supernatant liquid, a supply port of lower alcohol provided upstream of a catalytic reaction pipe and a mixing unit (50) to mix raw-material-oil fat or supernatant liquid and lower alcohol, and provided between supply port of lower alcohol and catalytic reaction pipe. The mixture of supernatant liquid from raw-material-oil fat or glycerin separation tank and lower alcohol is supplied from upper portion of the catalytic reaction pipe. The effluent from the lower portion of the catalytic reaction pipe is introduced into the glycerin separation tank.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the packed bed reactor. (Drawing includes non-English language text)    Multi-staged catalytic reaction pipe (10)    Pressure indicator (20)    Glycerin separation tank (40)    Mixing unit (50)    Reactor (100)