CANISTER

In a canister which includes a main chamber and a sub chamber divided by a partition plate and has an atmosphere port 14 formed on the upper surface of the sub chamber and communicating with the atmosphere and is used to process fuel vapor evaporated from the fuel tank of a vehicle, a first groove 15 is formed in such portion of the upper surface thereof as exists around the atmosphere port 14, two second grooves 16a and 16b are formed in the upper surface with their one-side ends connected to the first groove 15 and their other ends extended to the side surface of the canister, and a cap 18 having a wall portion 18c for closing one of the second grooves 16a and 16b is attached on the atmosphere port 14.