PURPOSE: To stabilize an oxygen lack type superconductor of an alkaline earth metal-rare earth-copper-oxygen system and to prevent the lack of oxygen with time, etc., by implanting fluorine ions to the oxygen lack type superconductor and annealing the superconductor under prescribed conditions.

CONSTITUTION: The oxygen lack type superconductor (e.g.; Ba2YCu3O) expressed by the formula (A is Ca, Sr, Ba; R is a rare earth element; 0≤x<3; n is a natural number; 0≤y<n) is prepd. This superconductor 3 is disposed in a sample system 16 of an ion implanting device and the ions generated from an ion source 11 are accelerated by an ion acceleration system 12. The fluorine ions are fractionated by a magnetic field in a mass analysis system 13 and are implanted to the point in the superconductor 3 where the oxygen is lacked, the point where the oxygen lack is liable to arise, etc. Such superconductor 3 is annealed for 1-3 hours at 850-950°C, by which the oxygen lack type superconductor having the stable superconducting characteristics is obtd.