PURPOSE: To improve the manufacturing method of a thin-film structure in such a way that the consistency of a silicon-IC manufacturing process is good and that the interval between a substrate and a movable part becomes large by eliminating a difference in level which causes a problem regarding a photolithographic technique.

CONSTITUTION: A silicon oxide film 12 is formed on the surface of a silicon substrate 11, the silicon oxide film 12 is removed partly so as to form a recessed part 13, and the silicon substrate 11 is exposed. A germanium layer 14 is grown selectively inside the recessed part 13 so as to flatten the surface, and a second silicon oxide film 15 is formed on the flat surface. An etching hole 16 which reaches the germanium layer 14 is made in the silicon oxide film 15, and only the germanium layer 14 is etches selectively from the hole 16 by using an M2O2 solution. Thereby, a hollow part 17 is formed, and a part to be used as a diaphragm 18 in the silicon film 15 is separated from the silicon substrate 11.