PROBLEM TO BE SOLVED: To reduce saprophytes in drain water.SOLUTION: A cultivation device (1) makes drain water circulate all day long in a circulation path of a drain water tank (32), an air conditioning device (35), and the drain water tank (32) through piping between the drain water tank (32) and the air conditioning device (35).SELECTED DRAWING: Figure 1COPYRIGHT: (C)2017,JPO&INPIT【課題】ドレン水中の雑菌を減少させる。【解決手段】栽培装置(1)は、ドレン水タンク(32)と空調装置(35)との間の配管を通じて、ドレン水タンク(32)、空調装置(35)、ドレン水タンク(32)の循環経路にてドレン水を一日中循環させる。【選択図】図1