PURPOSE: A hydrogen producing device using anaerobic microorganisms is provided to enhance hydrogen production efficiency to allow hydrogen-producing anaerobic microorganisms to use carbon monoxides when hydrogen is produced. CONSTITUTION: A hydrogen producing device (100) using anaerobic microorganisms comprises: a culture machine (110) which stores a culture medium containing hydrogen-producing anaerobic microorganisms; a circulation line (120) which is connected to the culture machine to discharge the culture medium from the culture machine and has a pump (121) for circulation of the culture medium; a carbon monoxide supply unit (130) which supplies carbon monoxides to the culture medium; a dissolution unit (140) with a tube which provides a delayed path for delaying time for dissolving the carbon monoxides; and a hydrogen collection unit (150) which captures hydrogen from gas separated from the culture medium. [Reference numerals] (130) Carbon monoxide supplying unit; (148) Control unit; (150) Hydrogen collecting unit; (160) Cooling unit; (170) Culture medium supplying unit