PROBLEM TO BE SOLVED: To provide a hydroponic apparatus, a plant factory, and a hydroponic method which are capable of effectively promoting growth of plants.SOLUTION: To achieve the objective, a hydroponic apparatus is employed which comprises: a nursery bed pallet for housing plants; a cultivation container filled with culture solution in which roots of the plants pulled out from a bottom surface of the nursery bed pallet are immersed; adjusting means for adjusting a gap between a water surface of the culture solution and the bottom surface of the nursery bed pallet. Particularly, the adjusting means adjusts the gap between the water surface of the culture solution and the bottom surface of the nursery bed pallet to allow roots of the plants in a range from 10% or more to 30% or less of the entire length to be exposed to air, by which root rot can be prevented to promote growth of plants.SELECTED DRAWING: Figure 1
