NOVELTY - Circulatory biomass energy recovery system, comprises culture section filled with liquid culture medium in which vegetable plankton is cultured as biomass material, biomass material recovery section, energy source conversion section, energy recovery section for recovering energy, and carbondioxide recovery section for returning carbondioxide into the culture section, where the energy source conversion section comprises methane fermentation section and section for producing hydrogen by photosynthetic bacterium using biomass material.    USE - For recovering circulatory biomass energy (claimed).    ADVANTAGE - The system efficiently recovers biomass energy at elevated levels.    DETAILED DESCRIPTION - Circulatory biomass energy recovery system, comprises (a) culture section (10) filled with liquid culture medium in which vegetable plankton is cultured as a biomass material, (b) biomass material recovery section (11) for recovering the biomass material from culture solution, (c) energy source conversion section (12) for converting the biomass material into an energy source from which energy can be recovered, (d) energy recovery section (13) for recovering energy from the energy source having bean converted in the energy source conversion section, (e) carbondioxide recovery section (14) for returning carbondioxide produced in the energy recovery section for returning carbondioxide produced in the energy recovery section into the culture section, where the energy source conversion section comprises methane fermentation section for conducting methane fermentation of the biomass material and hydrogen production section for producing hydrogen by photosynthetic bacterium using biomass material. An INDEPENDENT CLAIM is included for recovering circulatory biomass energy, involves culturing phytoplankton as biomass raw material in culture section containing culture solution, recovering the biomass raw material from culture section, converting the biomass raw material into energy source from which energy can be recovered, recovering energy from the energy source, recovering carbondioxide generated in the energy recovery process and transferred to a culture portion, where the energy conversion process generates methane by methane fermentation of the biomass material and hydrogen by hydrogen production section by photosynthetic bacterium using biomass material.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view representing the circulatory biomass energy recovery system. (Drawing includes non-English language text)    Culture section (10)    Biomass material recovery section (11)    Energy source conversion section (12)    Energy recovery section (13)    Carbondioxide recovery section (14)