The leakage diagnosis that carries out a leakage diagnosis on the basis of an internal pressure state of an airtight compartment by emitting gas from the compartment via a canister during a stop of the internal combustion engine includes; detecting a physical quantity that reflects a fuel adsorption state of the canister; and repeating the leakage diagnosis within the number of times of the leakage diagnosis, limited on the basis of the detected physical quantity. The compartment is formed in an evaporative fuel processing mechanism for an internal combustion engine. The evaporative fuel processing mechanism includes a fuel tank.