PROBLEM TO BE SOLVED: To provide a plant growth hydroponic device in which distance between a plant and a lighting device can be automatically adjusted so that proper intensity of the lighting for the plant is given according to a growth state of the plant.SOLUTION: In a plant growth hydroponic device, a projection 2a is formed on an undersurface of a cultivation plate 2. Two kinds of regions having different water levels are formed at a cultivation bed 1. A first region is a cultivation part 5 where water is held to dip a plant root at a high water-level, and a second region is a receiving columnar part 6 where the projection of the cultivation plate is held through water at a low water-level. As total weight of the cultivation plate 2 increase by growth of the plant, the projection 2a of the cultivation plate is submerged into water in the second region and the water-level of the first region is decreased, thereby sinking the cultivation plate 2 into the receiving columnar part 6 according to the growth of
