A canister comprises a tank port communicated with an upper air chamber in a closed fuel tank, a purge port communicated with an intake passage of an engine, an atmospheric port opened to the atmosphere, and a main adsorbent chamber containing activated carbon, and the canister is further provided with a partition plate between the tank port and the purge port for preventing both ports from being directly communicated with each other, so as to form a first chamber between the main adsorbent chamber and the tank port, and a second chamber between the main adsorbent chamber and the purge port, and a purge buffer plate is further provided in the main adsorbent chamber between the tank port and the purge port, for communicating between the first and second chambers with each other, the first chamber serves as an air chamber containing no activated carbon while the second chamber contains activated carbon. With this configuration, the canister has no external pipe line, the time change in fuel concentration of purged gas during treatment of evaporated fuel from the fuel tank is moderated in order to restrain an engine air-fuel ratio from being abruptly changed, and the operation ability of the engine can be satisfied.