PURPOSE: To shorten a fermentation time and to prepare an alcohol efficiently for a long time, by transferring partially a fermentation solution having a specific alcohol concentration from the first fermentation tank to the second fermentation tank, adding a new medium to the first fermentation tank, continuing the fermentation of both the tanks.

CONSTITUTION: A yeast culture subjected to yeast culture fermentation in the yeast culture tank 3 is fed to the first fermentation tank 5, a medium is added to it and the yeast culture is activated. At a stage when the alcohol concentration reaches 6W12wt%, 65W75wt% culture solution is transferred to the second fermentation tank 6. The fermentation tank 5 is charged with a new medium in the same amount as that transferred to the fermentation tank 6, 1/25W1/50 sterilized air based on the amount of liquid per minute is sent to it for 4W6hr, the fermentation is replaced by an anaerobic fermentation, and the fermentation is kept for 20W30hr.