PROBLEM TO BE SOLVED: To provide a moisture content observation device, a moisture content observation method, and a cultivation device with which it is possible to present a trend of moisture content included in a plant quantitatively in a sequence of time and contribute to early teaching about a state of water stress added to the plant or whether or not the plant is partly dead.SOLUTION: A first projection light source radiates a 905nm near infrared light having a characteristic of being not easily absorbed by a moisture content toward the leaves of a plant as reference light. A second projection light source radiates a 1550nm near infrared light having a characteristic of being easily absorbed by a moisture content toward the leaves of the plant as measurement light. A threshold setting/moisture index detection processing unit calculates a moisture index for one leaf that is a sum total ΣLn(I/I) of reflection intensity ratios. A control unit displays on a UI screen of a monitor a graph that represents the sum total and pixel average value of moisture contents of leaves as a time-series trend of moisture contents included in the leaves of the plant from the start time of a measurement period. On the leaves of the plant is arranged a white background plate that covers the back of the leaves of the plant as seen from the first projection light source and the second projection light source.SELECTED DRAWING: Figure 12【課題】植物に含まれる水分量の推移を定量的かつ時系列に提示し、植物への水ストレスの付与の状態や部分的に壊死していないかどうかの早期な教示に資する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、測定期間の開始時からの植物の葉に含まれる水分量の時系列の推移として、葉の水分量の総和と画素平均値とを表すグラフをモニタのＵＩ画面に表示する。植物の葉には、第１の投射光源及び第２の投射光源から見て、植物の葉の背面を覆う白色背景板が配置される。【選択図】図１２
