In a hollow seal member kept in abutted-engagement with a shaft hole formed in a housing via an elastic body and kept in sliding-contact with an outer circumference of a drive shaft for sealing against a leakage of fluid from a pump chamber, the seal member is provided with a seal part formed within an area at one end and kept in sliding-contact with the outer circumference of the drive shaft over a given hollow inner circumferential surface, and a rotation-stopping part formed within an area at the other end for restricting a movement of the seal member in a rotation direction of the drive shaft. A rotational resistance of the rotation-stopping part to the drive shaft is set to be less than a rotational resistance of the seal part.