PROBLEM TO BE SOLVED: To provide a water content observation apparatus, a water content observation method, and a cultivation apparatus which can flexibly control the water content in plants including fruits such as tomato in consideration of the effect of the surrounding environmental conditions.SOLUTION: A first projection light source irradiates the leaves of a plant with 905 nm near infrared light having a characteristic hard to be absorbed by water as a reference light. A second projection light source irradiates the leaves of a plant with 1550 nm near infrared light having a characteristic easy to be absorbed by water as a measuring light. The threshold setting/water index detection processing part calculates the water index of one leaf which is the sum of reflection intensity ratios ΣLn (I/I). The control part is connected to a control device that controls the environmental conditions around the plant, and instructs the control device to change or maintain an environmental condition based on the calculated change in the water content in the plant.SELECTED DRAWING: Figure 37【課題】周囲の環境条件の影響を考慮して、トマト等の果実を含む植物に含まれる水分量の制御を柔軟に行うことができる水分量観察装置、水分量観察方法及び栽培装置を提供する。【解決手段】第１の投射光源は、水分に吸収され難い特性を有する９０５ｎｍの近赤外光を参照光として植物の葉に向けて照射する。第２の投射光源は、水分に吸収され易い特性を有する１５５０ｎｍの近赤外光を測定光として植物の葉に向けて照射する。閾値設定／水分指数検出処理部は、反射強度比の総和ΣＬｎ（Ｉ９０５／Ｉ１５５０）である葉１枚の水分指数を算出する。制御部は、植物の周囲の環境条件を制御する制御装置と接続し、算出した植物に含まれる水分量の増減の推移を基に、環境条件の変更又は維持を制御装置に指示する。【選択図】図３７
