In the plant growth index measuring device, the plant growth index measuring method, and the plant growth index measuring system according to the present invention, each light of the reflected light of the measuring object having a plurality of leaves obtained by measuring at the first and second wavelengths. Growth in the measurement object based on the intensity, the solar angle that is the incident angle of the sunlight to the measurement object at the time of measurement, and the solar direction that is the direction of the sun with respect to the measurement direction of the reflected light A growth index that represents the degree of the above is obtained.本発明にかかる植物生育指標測定装置および植物生育指標測定方法ならびに植物生育指標測定システムでは、第１および第２波長で測定することによって得られる、複数の葉を持つ測定対象の反射光の各光強度、ならびに、その測定の際における太陽光の測定対象への入射角度である太陽角度、および、前記反射光の測定方向に対する前記太陽の方向である太陽方向、に基づいて、前記測定対象における生育の度合いを表す生育指標が求められる。
