A vegetation effect calculation device includes a memory configured to store instruction and at least one processor configured to execute the instructions to acquire a vegetation parameter being information indicating a characteristic of vegetation flourishing on a slope; and calculate vegetation adhesion per unit area and a total tree weight per unit area, based on the vegetation parameter, a first regression equation being a regression equation between a root diameter and an uprooting resistance, a second regression equation being a regression equation between a breast high diameter and a total tree weight, and a relationship between the uprooting resistance and vegetation adhesion.