NOVELTY - A sunlight utilization system (1) comprises hydrolyzing part (3) which decomposes electrolyte solution using sunlight energy which has a pair of electrode in which optical semiconductor catalyst is supported by one side, and is irradiated to optical semiconductor catalyst, fuel cell (20) which is electric-power-generated using hydrogen produced by disassembly of electrolyte solution, hydrogen storage part (31) which stores hydrogen obtained in hydrolyzing part, and oxygen storage part (33) which stores oxygen obtained in hydrolyzing part.    USE - A sunlight utilization system.    ADVANTAGE - Separate optimization of the utilization ratio of energy of fuel cell of hydrolyzing part, fuel cell part and sunlight utilization system is enabled.    DETAILED DESCRIPTION - A sunlight utilization system (1) comprises hydrolyzing part (3) which decomposes electrolyte solution using sunlight energy which has a pair of electrode in which optical semiconductor catalyst is supported by one side, and is irradiated to optical semiconductor catalyst, fuel cell (20) which is electric-power-generated using hydrogen produced by disassembly of electrolyte solution, hydrogen storage part (31) which stores hydrogen obtained in hydrolyzing part, oxygen storage part (33) which stores oxygen obtained in hydrolyzing part, hydrogen supply path which supplies hydrogen stored in hydrogen storage part to hydrogen electrode of fuel cell, oxygen supply path which supplies oxygen stored in oxygen storage part to air electrode of fuel cell, hydrogen supply control part which controls amount of hydrogen supplied to fuel cell from hydrogen storage part, and oxygen supply control part which controls oxygen amount supplied to fuel cell from oxygen storage part.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the structure of sunlight utilization system. (Drawing includes non-English language text).    Sunlight utilization system (1)    Hydrolyzing part (3)    Fuel cell (20)    Hydrogen storage part (31)    Oxygen storage part (33)