In a free energy difference estimation method, the partial free energy difference indicates a bound state between a target compound and a first candidate compound bindable to the target compound, and is stored in a storage part for each value of a binding constant. A change region, in which a partial free energy difference is equal to or greater than a predetermined change value, is specified in a region of the binding constant. The partial free energy difference of a second candidate compound in the change region is interpolated based on the partial free energy difference acquired in each of a previous region and a following region by using an approximation function.
