A holding jig (1, 2, 3) for a thin cylindrical work (W) includes a holding member (10, 10A, 10B) which holds the work (W) from an inner peripheral side and a diameter changing unit (25, 27) which changes a diameter of the holding member (10, 10A, 10B). The holding member (10, 10A, 10B) is made of metal and has a cylindrical shape and an elastically expandable or contractible diameter. The holding member (10, 10A, 10B) is configured with an outside diameter of the holding member (10, 10A, 10B) being held smaller than an inside diameter of the work (W) at the time of insertion into an inner periphery of the work (W) and being expanded after inserted into the inner periphery of the work (W) to hold the work (W) from an inner peripheral side of the work (W) with an outer peripheral surface in close contact with an entire inner peripheral surface of the work (W). The diameter changing unit (25, 27) applies at least one of an axial external force in a compressing direction or an axial external force in a tensile direction to both ends of the holding member (10. 10A, 10B) to change the diameter of the holding member (10, 10A, 10B).