The present invention includes a first canister disposed within an intake air passage. The first canister communicates with a fuel tank via a second canister, so that a fuel vapor produced within the fuel tank can be purged by the second canister and further by the first canister. The second canister communicates with the intake air passage via a purge passage. The negative pressure within the intake air passage may be applied to the first and second canisters via the purge passage, so that the fuel vapor adsorbed by the first and second canisters can be desorbed or purged and can then be returned into the intake air passage.