A leaf area index measurement system includes: imaging means for capturing an image of a measurement target plant and outputting the captured image； a light source placed either on a side of the measurement target plant opposite to the imaging means or at a position of the measurement target plant； intensity calculation means for calculating an intensity of light when the light source emits light, based on the captured image output from the imaging means； and leaf area index calculation means for calculating a leaf area index, based on the intensity of light calculated by the intensity calculation means.
