A hydroponic device (100) equipped with: a cultivation tank (3) for cultivating a plant (1) a cultivation medium (2) that has flexibility and liquid retention properties and guides the elongation of an underground part (1a) toward a direction crossing the vertical direction and a supporting part (10) that is disposed in the cultivation tank (3) and supports the cultivation medium (2) so as to maintain the state where the elongation of the underground part 1a is guided along the direction crossing the vertical direction.