A device capable of capturing the influence of vegetation on slope stability is provided. The vegetation effect calculation device is a first equation that is a regression equation of an acquisition unit that acquires vegetation parameters that are information indicating characteristics of vegetation that grows on a slope, and a vegetation parameter, a root diameter, and a root removal resistance acquired by the acquisition unit. Based on the regression equation, the second regression equation that is a regression equation of the breast height diameter and the total tree weight, and the relationship between the root resistance and the vegetation adhesive force, the vegetation adhesive force per unit area and the total per unit area A vegetation influence calculating unit for calculating the tree weight is provided. 植生が斜面の安定性に与える影響を捉えることが可能な装置を提供する。植生影響算出装置は、斜面に繁茂する植生の特性を示す情報である植生パラメータを取得する取得部と、取得部が取得した植生パラメータ、根元直径と抜根抵抗力との回帰式である第１の回帰式、胸高直径と全木重量との回帰式である第２の回帰式、および、前記抜根抵抗力と植生粘着力との関係に基づき、単位面積あたりの植生粘着力および単位面積あたりの全木重量を算出する植生影響算出部を備える。
