A plant-culturing tool comprising a plant container for storing a plant and a water storage container capable of storing the plant container therein and capable of storing water. The plant-culturing device further includes a guide mechanism for guiding the plant container by bringing the plant container into slidable contact with the water storage container along its floating/sinking direction. The guide mechanism includes a long guide face with a long slidable contact part and a short guide face with a short slidable contact part projected toward the long guide face which are brought into slidable contact with each other.