PROBLEM TO BE SOLVED: To accurately measure the water content in a plant that is an index of a degree of health of the plant.SOLUTION: A first projection beam source of a plant detection camera 1 radiates a near infrared beam (reference beam) with a first wavelength (905 nm), characterized by being hardly absorbed in water, toward a leaf PT3 of a plant PT by optical scanning. A second projection beam source of the plant detection camera 1 radiates a near infrared beam (measuring beam) of a second wavelength (1550 nm) characterized by being easily absorbed in water toward the leaf of the plant PT by optical scanning. A threshold setting/water content index detection processing unit calculates the water content index of one leaf that is a total sum ΣLn(I/I) of the reflection intensity ratio on the basis of a reflection beam of 905 nm reflected at all irradiation positions of the leaf and a reflection beam of 1550 nm reflected at all irradiation positions of the leaf.SELECTED DRAWING: Figure 1【課題】植物の健全度の指標となる植物に含まれる水分量を正確に測定する。【解決手段】植物検出カメラ１の第１の投射光源は、光学走査により、水分に吸収され難い特性を有する第１波長（９０５ｎｍ）の近赤外光（参照光）を植物ＰＴの葉ＰＴ３に向けて照射する。植物検出カメラ１の第２の投射光源は、光学走査により、水分に吸収され易い特性を有する第２波長（１５５０ｎｍ）の近赤外光（測定光）を植物ＰＴの葉に向けて照射する。閾値設定／水分指数検出処理部は、葉の全照射位置において反射した９０５ｎｍの反射光と葉の全照射位置において反射した１５５０ｎｍの反射光とを元に、葉１枚の反射強度比の総和ΣＬｎ（Ｉ９０５／Ｉ１５５０）である水分指数を算出する。【選択図】図１
