NOVELTY - The apparatus has a container (2) that is provided to accommodate liquid (1) containing water, and photochemistry electrode plates (3). The container is equipped with a supply port (14) to supply liquid containing water, and a gas output opening to take out gas by which photochemistry electrode plate decomposes and produces water. A light irradiation unit (4) is arranged in a gap of photochemistry electrode plates arranged face to face to irradiate light toward surface of electrode plate. A space where the liquid exists is arranged between the irradiation unit and electrode plate.    USE - Gas-making apparatus.    ADVANTAGE - The light irradiation unit is arranged in gap of photochemistry electrode plates arranged face to face to irradiate light toward surface of electrode plate, thus the gas-making apparatus irradiates light to surface of photochemistry electrode efficiently and generates gas by photochemical reaction, and the small occupied by gas-making apparatus is reduced.    DETAILED DESCRIPTION - The photochemistry electrode plates are respectively with photo-catalyst layer having photo-catalyst effect at one surface, and gap that is opened into container. The light irradiation unit is provided with a light-guide plate that emits light while light-guiding the light injected into edge portion of main portion, and an optical fiber whose end is connected to edge portion of light-guide plate and other end is withdrawn by exterior of container. The optical fiber is provided to guide the light from an external light source to light-guide plate. The unevenness which diffuses the light to radiate is formed in surface of light-guide plate. The light irradiation unit is provided with a flow path of a liquid light source, and the flow path is formed of material which permeates the light emitted by liquid light source. The photo catalyst layer is formed as nitride semiconductor layer, and equipped with some protrusion on surface. One portion of photo catalyst layer is formed of gallium nitride, and other portion is formed of indium gallium nitride. The carrier concentration of the single-crystal layer in nitride semiconductor layer is higher than carrier concentration of protrusion. Electrode pad is arranged at portion of single-crystal layer. The container is partitioned off into first chamber and second chamber. The photochemistry electrode plate, light irradiation unit, and gas output opening are arranged in first chamber. The photochemistry electrode plate and metal electrode are connected to second chamber by conducting wire. The second chamber is equipped with a second gas output opening which takes out the gas by which the metal electrode decomposes and produces the water.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram illustration the gas-making apparatus. (Drawing includes non-English language text)    Liquid (1)    Container (2)    Photochemistry electrode plate (3)    Light irradiation unit (4)    Supply port (14)