In the present invention, a sealed space, excluding one part which is an unsealed portion, is formed by making a wall surface and bottom surface of a container into an integrated double-layered structure, the sealed space serving as a water storage tank, and a lower-part space inside the container, surrounded by the water storage tank, serving as a water collection section. The device is provided with a water supply duct, the upper end of which, i.e. a water injection port, is open to the exterior and is positioned in the vicinity of the upper part of the water storage tank, and the lower end of which, i.e. a water discharge port, is open in the vicinity of the lowermost surface inside the water storage tank. A contact section between the water storage tank and the outer periphery of the water supply duct is a sealed structure. The device is provided with a ventilation duct, the upper end of which is open to an upper space inside the water storage tank and the lower end of which is open in the vicinity of the lowermost surface inside the water storage tank. A contact section between the water storage tank and the outer periphery of the ventilation duct is a sealed structure. A water passage opening is provided at at least one location, the water passage opening penetrating into the water storage tank from the bottom of the water collection section. A water passage tool composed of a water-permeable, water-absorbent resin is tightly adhered and mounted onto the water passage opening. This makes it possible to maintain a substantially constant water level in the water collection section until the water in the water storage tank is substantially exhausted. Consequently, it is possible to raise healthy plants inside a planter that is installed inside the water collection section and that has a water discharge port (=water intake) at the bottom thereof, and to simultaneously realize long-term bottom watering with the simple act of merely pouring water into the water stor
