PURPOSE: To prepare ethanol in high productivity and fermentation ratio, by fermenting starch using a starch-fermentation yeast having two kinds of starch fermentation governing genes in a cell.

CONSTITUTION: Starch is fermented by using Saccharomyces diastaticus BC3 strain (FERM-P No.6708) containing the starch fermentation governing genes STA2 and STA3 in one cell, having improved ethanol productivity from starch, and obtained by the cell fusion of Saccharomyces diastaticus 4C strain (FERM-P No.6706) and 17B strain (FERM-P No. 6707). Ethanol can be prepared directly in high productivity and high fermentation ratio.