PROBLEM TO BE SOLVED: To provide a carbon dioxide fertilization device that can control the amount of carbon dioxide supplied to an optimal level according to the state of photosynthesis of plants.SOLUTION: The carbon dioxide fertilization device: determines the state of photosynthesis a plant 23 on the basis of the temperature difference between a leaf vein part 34 and a lamina part A of the plant 23 and the time of day； determines the speed of photosynthesis of the plant 23 on the basis of the difference between the temperature within the agricultural facility and the leaf temperature of the plant 23； and controls the amount of carbon dioxide supplied into the agricultural facility to raise the plant 23 on the basis of the state of photosynthesis of the plant 23 using the determined speed of photosynthesis of the plant 23 as an indicator.SELECTED DRAWING: Figure 2【課題】本発明の目的は、植物の光合成の状態に合わせて、最適な二酸化炭素の供給量の制御を行うことができる二酸化炭素施肥装置を提供する。【解決手段】植物２３の葉脈部３４と葉身部Ａとの温度差と時刻とに基づいて、植物２３の光合成の状態を判定し、農業施設内の温度と植物２３の葉温との温度差に基づいて植物２３の光合成の速度を判定し、判定した植物２３の光合成の速度を指標として、植物２３の光合成の状態に基づいて、植物２３を生育させる農業施設内への二酸化炭素の供給量を制御する二酸化炭素施肥装置。【選択図】図２
