A vegetation effect calculation device includes: a memory configured to store instructions； and at least one processor configured to execute the instructions to: acquire a moisture content of a slope, a relational expression between the moisture content and an adhesion of soil in the slope, and a vegetation adhesion that is an adhesion of vegetation abundantly growing in the slope； calculate a correction value, using the acquired moisture content of the slope, and the acquired relational expression between the moisture content and the adhesion of the soil； and calculate a corrected vegetation adhesion, using the acquired vegetation adhesion, and the calculated correction value.
