A hydroponic device (100) comprising: a ground surface section (12) being provided with a throughhole (12a), into which a plant (10) is to be inserted, and partitioning an underground space (11a), in which the underground part (10b) of the plant (10) grows, from an above-ground space (1121), in which the above-ground part (10d) of the plant (10) grows； a culture tank (11) forming, together with the ground surface section (12), the underground space (11a) so as to enclose the underground part (10b) therein； germination prompting agent supply sections (1000, 2000) supplying a germination prompting agent (3), which is stored in a germination prompting agent storage section (30), to the above-ground parts (10d, 20d) and/or the underground parts (10b, 20b)； and a controller (40) controlling the mode in which the germination prompting agent supply sections (1000, 2000) supply the germination prompting agent (3) to the plants (10, 20).
