PURPOSE: To improve the starting properties of an engine, by mounting an outer vent control valve for closing and opening a fuel vapor passage in response to the ON-OFF of an ignition switch.

CONSTITUTION: Since a temperature valve 13 is opened and an outer vent control valve 6 is also opened when a car is brought to a dead soak condition by switching an ignition switch 7 OFF after the car travles, the vapor of fuel generated at a float chamber of a carbureter 1 is sufficiently adsorbed by means of a charcoal canister 11. When an engine is restarted under the dead soak condition, the vapor of fuel adsorbed to charcoal canisters 11, 12 is purged by atmospheric air sucked from atmospheric air ports 11b, 12b and introduced at the downstream side of a throttle valve 1c of the carbureter 1, but the air fuel ratio of mixture does not reach over- rich.