A hydroponic device provided with: a cultivation tank (1)； a culture medium part (21) that comprises a tabular elastic body having a slit (210), and that supports a plant in the slit (210)； and a holding part (2) that has a hole part (20) having a smaller area than the culture medium part (21) in a plan view, and that holds the culture medium part (21) in the hole part (20) such that the roots of a plant (P) are located inside the cultivation tank (1). The upper surface of the culture medium part (21) has marker parts (22) with a visually recognizable shape.
