TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Process: The microorganism further possesses the formate dehydrogenase gene. The microorganism is a facultative anaerobic bacterium, where the facultative anaerobic bacterium is a transformant of E. coli. The microorganism possesses the inactivated lactate dehydrogenase gene and the inactivated at least one of the genes encoding the subunits which make up of the fumarate reductase. The microorganism is the W3110 Delta ldtLA Delta frdBC strain of E. coli (deposited with International Patent Organism Depositary Authority, National Institute of Advanced Industrial Science and Technology of Japan under the accession No. FERM P-20737 and the international accession No. FERM BP-10726). The microorganism is cultured under aerobic conditions and then further cultured under anaerobic conditions. The organic substrate is saccharides, where the saccharides are glucose, galactose, xylose, sucrose and fructose. EXAMPLE - The ldhA- and frdBC-inactivated strain were obtained and was added to 10 mL of the culture medium and cultured under shaking overnight at 37degrees C under aerobic conditions. A 10 mL of the culture medium containing the ldhA- and frdBC-inactivated strain as cultured under shaking overnight was inoculated onto 1.0 L of the culture medium, followed by culture under anaerobic conditions. Cultivation under anaerobic conditions was performed in the anaerobic chamber system having an atmosphere of 95% nitrogen and 5% hydrogen. The culture under anaerobic conditions was conducted for 12 hours at 37degrees C, while maintaining the culture medium at pH 6.0. The resultant culture medium was subjected to a centrifuge, followed by removal of the supernatant to give 4 g (wet weight) of microbial cells. The resultant microbial cells were suspended in 100 mL of a solution for the hydrogen generation in such a manner that the cell density might be 4% (on the basis of microbial cell mass in the wet state). The thus-prepared microbial cell suspension for the hydrogen generation was admixed with a 3M aqueous solution of glucose under anaerobic conditions, and the hydrogen generating capability of the microorganism was evaluated. The gas evolved immediately after addition of glucose, and the initial rate of hydrogen generation was determined from the volume of the gas generated in 10 minutes after addition of glucose. Analysis by gas chromatography of the generated gas as collected revealed that the generated gas contains ca. 60% by volume of hydrogen and ca. 40% by volume of a gas (carbon dioxide gas).