PROBLEM TO BE SOLVED: To provide a carbon dioxide gas application device and a carbon dioxide gas application control method which appropriately apply carbon dioxide gas to a thickly grown part of cultivated crops by controlling application timing, an application position and an application amount of carbon dioxide gas in a sunlight type greenhouse which performs skylight window opening and wall surface ventilation fan operation based on a set air temperature.SOLUTION: In a carbon dioxide gas application control device and a carbon dioxide gas application control method, in a state where a time zone determined by a timer comes, and a skylight window is closed and wall surface ventilation fans do not operate, carbon dioxide gas is applied from under a thickly grown part of a rack of cultivated crops to maintain carbon dioxide gas concentration of the thickly grown part within a fixed concentration range by a carbon dioxide gas concentration meter and control of a sequencer or a relay. In a case where the skylight window is opened, application of the gas is stopped, and outflow of carbon dioxide gas caused by air replacement through the skylight window opening is suppressed. When air temperature rises even higher to cause a state where the wall surface ventilation fans start operating to vent out air in a greenhouse from the wall surface, application of the gas from under the thickly grown part is stopped, positions from which the gas is applied are appropriately installed on the windward side of the thickly grown part and carbon dioxide gas is applied to the thickly grown part, and carbon dioxide gas concentration of the thickly grown part can be maintained within a fixed concentration range by the carbon dioxide gas concentration meter and control of the sequencer or the relay.【課題】本発明は設定気温によって天窓開口や壁面換気扇稼働を行う太陽光型ハウスにあって炭酸ガスの施用タイミング、施用位置、施用量を制御することで栽培作物の繁茂部分に炭酸ガスを適正に施用する炭酸ガス施用装置と施用制御方法を提供する。【解決手段】タイマーで決定された時間帯となり壁面換気扇が稼働しない状態で天窓が閉じた状態では、栽培作物の棚の繁茂部分の下から炭酸ガスを施用し、炭酸ガス濃度計
