TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In (M1), the oxidation-reduction potential of the formic acid-containing culture solution is maintained during the anaerobic condition, in a range of -200 mV to -500 mV, where the range of oxidation-reduction potential of solution for hydrogen generation in a reduced state, is -100 mV to -500 mV. In (b) of (M1), the organic substrate is formic acid, formate or a compound, which is converted into formic acid by metabolism in microbial cells.The concentration of microbial cells in solution for hydrogen generation in the reduced state, is 0.1-80% (w/w) (wet-condition microbial cell mass reference (standard)).The pH of the solution for hydrogen generation, is maintained at 5.0-9.0, and the organic substrate is supplied continuously. EXAMPLE - Generation of hydrogen by microorganism such as Escherichia coli W strain (ATCC 9637) was carried out as follows. The microorganism was inoculated into a culture solution (500 ml) containing water (1000 ml), tryptone (10 g), yeast extract (5 g) and sodium chloride (5 g). The organisms were cultivated under aerobic conditions at 37 degrees C, overnight. The microbial cells were obtained by centrifugation for 15 minutes. The obtained microbial cells were suspended into induction culture medium (6 L) containing water (1000 ml), yeast extract (0.5%), tryptone/peptone (1.0%), molybdic acid soda anhydride (10 microM), selenious acid soda pentahydrate (10 microM), glucose (20 mM), sulfate of soda (0.05%), formic acid soda (5 mM), etc., where from the induction culture medium, the oxygen was removed under pressure reduction conditions at 4.00x10 to the power 2 Pa. When the concentration of the microbial cells increased as measured by spectrophotometer (initial OD at 610 nm was 1.5 and after cultivation under anaerobic conditions was 3.7), the culture solution was subjected to centrifugation for 12 minutes, and the microbial cells were recovered. The obtained microbial cells were transferred into a solution (50 ml) for hydrogen generation, containing water (1000 ml), yeast extract (0.5%), tryptone/peptone (1.0%), molybdic acid soda anhydride (10 microM), selenious acid soda pentahydrate (10 microM), antifoaming agent (0.1%), etc. Formic acid was continuously supplied to the solution, and the pH was maintained nearer to 6.5, by phosphoric acid buffer agent. The oxidation-reduction potential immediately reduced from -200 mV during hydrogen generation, and was later maintained nearer to -390 mV. Gas was produced simultaneously during the supply of formic acid. The gas production velocity was measured and was found to be 92 ml/minute. When the collected gas was subjected to gas chromatography, it was found to contain 49% of hydrogen and residual carbon dioxide. The hydrogen generation velocity was found to be 54 L (H2)/hour/L.