a fuel supply passage 3 to a fuel injection valve 4 as a fuel supply means provided in an internal combustion engine e a charge passage 8 is connected to an upper space within the fuel tank t and also through a canister c to a purge passage 9 which is connected to that portion of an intake passage 5 in the engine e which is downstream of a throttle valve 6 the canister c is of an open bottom type with its lower end opened the canister c comprises a pair of upper and lower filters 10 10 and an activated carbon 11 serving as an adsorbent accommodated between the filters 10 10 the charge passage 8 on the side of the fuel tank t is opened into the activated carbon 11 and the purge passage 9 on the side of the internal combustion engine e is opened into a space above the upper filter 10 a space below the lower filter 10 is opened to the atmosphere through an atmosphere opening passage 12 a two way valve 13 is provided in the middle of the charge passage 8 the valve 13 is opened when the internal pressure in the fuel tank t is increased to exceed the atmospheric pressure by a predetermined value and when the internal pressure in the fuel tank t is reduced to a level lower than the internal pressure in the canister c by a predetermined value thereby providing the communication between the fuel tank t and the canister c when evaporated fuel from the canister c is purged into the intake passage 5 the charge passage 8 at the side of the canister c may.