A plant cultivating device (A), comprising aluminum long square pipe trays (5) for storing plants (35) together with culture solution, a conveyor device (2) for feeding the trays (5) in order in lateral direction, and a lighting device (3), having a number of light-emitting diodes disposed thereon, located over the conveyor device (5), the lighting device (3) being disposed so as to be higher gradually from the upstream side to the downstream side of the conveyor device (2), wherein a funnel-shaped holder (30) holding the upper part of the plant (35) is provided on the upper surface of the tray (5), and a planting conveyor (6) and a harvesting conveyor (7) for supply and retrieval, a reflecting wall (8) provided between these conveyors and the conveyor device (2), and transfer bars (41) for transferring the trays (5) between the conveyor device (2) and the planting and harvesting conveyors (6,7) are installed on the upstream and downstream sides of the conveyor device (2).