NOVELTY - A light water electrolysis apparatus has light energy converter (11), counter electrode reaction portion, connection portion, gas storage portion (3) and control portion. At least one portion of reaction portion is formed using porous conductive material (12). Light energy converter produces hydrogen or oxygen by electrolyzing water. Reaction portion produces hydrogen or oxygen by counter electrode reaction. Control portion detects generation rate of gas, and adjusts distance between water surface and energy conversion portion, such that generation rate is maximum.    USE - For producing hydrogen and oxygen.    ADVANTAGE - The electrolysis apparatus has improved energy conversion efficiency. The distance between the photocatalyst portion and water surface is simply controlled.    DETAILED DESCRIPTION - A light water electrolysis apparatus has a light energy converter (11), a counter electrode reaction portion, a connection portion for connecting light energy converter and counter electrode reaction portion, a gas storage portion (3) and a control portion. At least one portion of reaction portion is formed using porous conductive material (12). The light energy converter produces hydrogen or oxygen by electrolyzing water using light energy. The reaction portion produces hydrogen or oxygen by counter electrode reaction of electrolysis reaction in energy conversion portion. The connection portion is provided at vertical upward direction of reaction portion. The gas storage portion stores the gas generated from reaction portion. The control portion detects generation rate of gas in reaction portion, and adjusts the distance between water surface and energy conversion portion, such that the generation rate is maximum. An INDEPENDENT CLAIM is included for control of light water electrolysis apparatus.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional view of structure of light water electrolysis apparatus. (Drawing includes non-English language text)    Water retention tank (1)    Hydrogen storage portion (3)    Photocatalyst portion (11)    Porous conductive material (12)    Solar cell (13)