PURPOSE: To reduce the motion of a clamp ring while an air spring is operated by surely providing a ring on one of end members by a pair of annular projections on the annular seal surface and a pair of recesses of the clamp ring, and receiving a sleeve in three grooves in the seal surface of the other end member.

CONSTITUTION: A pair of annular projections 19, 20 which are spaced from each other in the axial direction and extend outward in the radial direction are formed on an annular seal surface 10, and a pair of recesses 33, 34 are formed in a clamp ring 32, and the ring 32 is surely provided on end members 3 in a joint manner. A pair of tightening regions are provided which are spaced from each other in the axial direction to hold a flexible sleeve 8, and in addition, the traveling direction of a reinforcing cord 9 in the end of a sleeve 8 is changed, and at least three grooves 23, 26, 27 to provide an expansion region on the seal surface of one of the end members 3 are formed, the elastic material of the sleeve 8 is received therein, and one groove is arranged between a pair of projections, and the other two grooves are arranged on the other side of the projections. This constitution reduces the motion of the clamp ring while an air spring is operated.