A leak hole determination device in an evaporated fuel processing system. The leak hole determination device includes: a first pressure detector for detecting a first pressure in a fuel tank; a second pressure detector for detecting a second pressure in a canister; and a leak hole determiner for determining whether a leak hole is present. The leak hole determiner determines, after a limit pressure timing subsequent to a depressurization operation for depressurizing an inside of the system, whether a leak hole is present by using a difference between a change speed of a first pressure detected by the first pressure detector and a change speed of a second pressure detected by the second pressure detector.