Abstract: A fuel-vapor emission control apparatus is mounted on a vehicle having an internal combustion engine and a fuel tank. The engine has a plurality of cylinders and is supported by engine mounts. The fuel-vapor emission control apparatus purges fuel-vapor in the fuel tank and supplies the purged fuel-vapor to the engine. The apparatus includes a vacuum switching valve, sensors and an electronic control unit. The vacuum switching valve controls the amount of purged fuel-vapor that is supplied to the engine. The sensors detect the operating state of the engine. The electronic control unit duty controls the vacuum switching valve in accordance with data from the sensors. The control unit also serves to suppress resonance of the engine and the engine mounts when purged fuel-vapor is being supplied to the engine.