The effects of ultrasonic wave irradiation on cell growth and the formation of ethanol and other volatile components in the fermentation process were investigated. The fermentation periods were reduced to 50-64% in wine, beer, and sake made from saccharified rice solution when weak ultrasonic waves were irradiated at 30 nW/cm2; the total intensity was 590 mW. YEPD medium fermented by a combination of optimal thermal trajectory control and continuous ultrasonic irradiation yielded a concentration of isoamylacetate about 2.5 times greater than the maximum concentration under isothermal conditions (20-degrees-C). Irradiation had virtually no effect when the dissolved carbon dioxide concentration (DCO2) was maintained at a level lower than the experimental value of Bunsen’s CO2 absorption coefficient. Therefore, it is suggested that irradiation accelerates the formation of ethanol and other components mainly by decreasing DCO2.