An oil seal has a lip seal member, a slinger and a dust cover. The slinger has a thread groove carrying out a pumping action toward a diametrically outer side. The dust cover achieves a dust shake-off action by a centrifugal force at the shaft rotating time, and a labyrinth seal action by forming a micro gap in relation to the lip seal member. The lip seal member has a main lip and a dust lip. The elastic dust lip has a first bellows portion receiving an atmospheric pressure by an inner surface and receiving an internal pressure between the lips by an outer surface, a second bellows portion receiving the atmospheric pressure by an outer surface and receiving the internal pressure between the lips by an inner surface, and a lip end. A pressure receiving area of the first bellows portion is greater than the second bellows portion.