To prevent the deformation of a soft fixed member by imparting tension to a clamping sheet surrounding the outer periphery of the soft fixed member, so as to clamp the fixed member while surrounding specific percentage of the outer periphery of the fixed member.

An expansion chuck 10 holding a fixed member 7 is placed in a clamping sheet 5 positioned in a control hole 2. In this state, two tension generators 6 are moved inward to apply pressure in an inner diameter direction while surrounding the most part of the whole peripheral surface (at least 75% or more of the whole periphery) of the expansion chuck 10 by the clamping sheet 5. The expansion chuck 10 is therefore strained so as to hold the outer peripheral surface of the fixed member 7 firmly with uniform pressure. The expansion chuck 10 is formed of soft material easy to elastically deform and brought into close contact with the whole outer peripheral surface of the fixed member to apply pressure uniformly through the inner surface of claw parts 12 at the time of being strained, so that the outer peripheral surface of the fixed member 7 is not deformed.