An ethanol production system, which is an integrated bioreaction for the production of ethanol from CO2, was developed. This system consists of biochemical and chemical reaction processes for the following: (i) photosynthetic CO2 fixation and biomass production of cyanobacterium Synechococcus leopoliensis, (ii) HCl-catalyzed saccharification of cyanobacterial biomass to glucose, and (iii) ethanol fermentation of yeast Saccharomyces sake using glucose, which is extracted from cyanobacterial biomass as the substrate. We successfully converted the CO2-derived glucose to ethanol using this system, which also enhanced the activities of S. sake for glucose consumption and for ethanol production.