Abstract: An improved fuel tank apparatus for use in a vehicle having a filler lid provided in a body of the vehicle includes a fuel tank in which fuel is to be stored, a filler tube connected to the fuel tank for introducing fuel into the fuel tank, a filler cap removably attached to an inlet port of the filler tube, a canister for absorbing and treating evaporated fuel generated in the fuel tank, an evaporation tube connected between the fuel tank and the canister, a check valve provided in the evaporation tube for releasing the evaporated fuel to the canister when pressure inside the fuel tank exceeds a predetermined level due to evaporation of the fuel in the fuel tank, and a mechanism for releasing the evaporated fuel which remains within the fuel tank due to the pressure inside the fuel tank being less than the predetermined level into the canister. The releasing mechanism is operated only when the filler lid is opened under the condition that the filler cap if closed.