A seat member has a seat portion, a receiving surface of which comes into contact with a bearing surface of an end turn portion, a mounting shaft portion protruded from the receiving surface of the seat portion, and an enlarged diameter portion formed at the front end of the mounting shaft portion for guiding press-fitting, in a cross section along an axial direction of a coil spring, an outer diameter of the enlarged diameter portion is set larger than an inner diameter of the end turn portion and an axial length of the enlarged diameter portion is set so that at least a maximum diagonal length of the seat member is larger than an inter-element wire distance.