PURPOSE: To form a magnetic bubble garnet film being free from magnetic defects and having the improved adhesiveness to a photomask, by making the surface of the garnet film flat.

CONSTITUTION: After a garnet film 2 having a composition of (YSmLuCa)3 (FeGe)5O12 is formed on a Gd3Ga5O13 substrate 1 by the epitaxial growing method, YAG laser beams are applied, on the conditions of a pulse width of 10ns and a power intensity of 2×10W8att/cm2, onto the parts of the garnet film 2 whereon a thick-film part 2a and a minute covex part 2b are formed so as to remove these parts 2a and 2b and thereby to make the film 2 flat, and thereby the whole of the garnet film 2 is formed to have a uniform thickness. Since the surface of the garnet film can be made flat in this way, it is made entirely free from magnetic defects. At the same time, the adhesiveness of the film to a photomask is improved, and thereby the occurrence of damage is eliminated. Thus, the yield of a magnetic bubble memory element can be improved sharply.