Provided is a device capable of capturing the effect that vegetation has on the stability of a slope. A vegetation effect calculation device comprising: an acquisition unit that obtains vegetation parameters being information indicating the features of vegetation flourishing on a slope; and a vegetation effect calculation unit that calculates the vegetation adhesion per unit area and the total tree weight per unit area, on the basis of vegetation parameters obtained by the acquisition unit, a first regression equation being a regression equation for the root diameter and uprooting resistance force, a second regression equation being a regression equation for diameter at breast height and total tree weight, and the relationship between the uprooting resistance force and the vegetation adhesion.
