A fuel evaporative emission treatment system installed in an engine fuel system has a canister for adsorbing evaporative fuel, a vent hose connecting a fuel tank and the canister, and a vent circulation hose connecting the vent hose and a filler neck of the fuel tank, and the sectional areas of the vent hose and vent circulation hose are set so that the ratio thereof may be a proper value. The negative pressure produced in the filler neck due to aspiration induced by refueling is canceled out by the pressure of fuel gas circulated to the filler neck through the vent circulation hose, whereby the internal pressure of the filler neck is controlled to a value appropriately smaller than the atmospheric pressure. Thus, inflow of the outside air into the filler neck, and thus generation of evaporative fuel gas, can be suppressed, and also the outflow of evaporative fuel gas from the filler neck is suppressed.