PURPOSE: To prevent evaporation fuel from leaking to the outside by closing a first atmosphere introducing passage by means of an opening/closing valve in start of an engine, and by providing a evaporation fuel leakage preventing mechanism in a second atmosphere introducing passage.

CONSTITUTION: Evaporaation fuel generated in a fuel tank 6 during stop of an engine is adsorbed and held on the way of a vent passage 8 for communicating the inside of the fuel tank 6 with the air-intake system of the engine 4. While a canister 10 for separating and supplying evaporation fuel adsorbed and held by new air-introduced from an atmosphere introducing passage 22 during drive of the engine is provided. Moreover, first and second atmosphere introducing passages 22-1, 22-2 are formed by branching the atmosphere introducing passage 22. An opening/closing valve 24 to be closed when the engine 4 is started is provided in the first atmosphere introducing passage 22-1, while an evaporation fuel leakage preventing mechanism 28 is provided in the second atmosphere introducing passage 22-2. Therefore, evaporation fuel can be prevented from leaking from the atmosphere introducing passage 22 of the canister 10 when the engine 4 is started.