The present invention provides a heat-curable silicone rubber composition having antistatic properties, even after secondary vulcanization at high temperatures. The power transfer unit includes an input portion, an output portion, a parallel gear set, a non-parallel gear set and a front wheel differential all enclosed within a common housing as an integrally packaged assembly. The cleaning device has a main body pivotable about one end thereof relative to an outer bottom surface of the water tank, a brush provided on the other end of the main body, and a bias spring for biasing the main body toward an opening direction.