A fuel vapor processor has a fuel tank configured to reserve fuel, a canister containing adsorbent capable of adsorbing fuel vapor vaporized in the fuel tank, a separator receiving a fuel vapor containing gas from the fuel tank, a regulator controlling the volume of the fuel vapor containing gas supplied to the separator, and a suction unit capable of removing the fuel vapor from the canister. The separator selectively passes the fuel vapor therethrough in order to divide the fuel vapor containing gas into a first gas mainly containing the fuel vapor and a second gas having a fuel vapor density lower than the first gas. The suction unit suctions the first gas from the separator in order to return the first gas into the fuel tank. The second gas is introduced into the canister or is released into the atmosphere.