To adjust the inside diameter of a part for holding at least a cushioning member of a cylindrical member appropriately, and hold appropriately by press-inserting a pillar wounded with the cushioning member into the cylindrical member.

The cushioning member is compressed by pressing the cushioning member in the direction perpendicular to the axis of the pillar by a pressing body 9 in a state of winding the cushioning member (cushion mat 3) at the outer periphery of the pillar (catalyst carrier 2), the surface pressure of the cushioning member against the pillar is detected, and the predetermined distance between the axis of the pillar and the end of the pressing body is measured when the surface pressure reaches a predetermined value. The pillar wounded with the cushioning member is press-inserted into the cylindrical member of which the diameter is previously contradicted or expanded so that the actual diameter of the inside of the part holding at least the cushioning member becomes the predetermined distance.