A fixture includes a base portion and a pair of holding portions on the base portion. Each holding portion include a clamping portion for clamping an object, and a head portion on the clamping portion side opposite to the base portion side. Each head portion includes a through-hole for a fastening member for adjusting a gap between the holding portions. The rigidity of the clamping portions is smaller than the rigidity of the head portions, with respect to deformation caused by the fastening member. The distance from the base portion to end portions of the holding portions in a plane orthogonal to the axial direction of the object is determined according to the tolerance prescribed for the object. The gap when external force is not being applied by the fastening member is determined according to an allowable amount of stress to be applied to the object.