PURPOSE: To provide an air micromachining method and a sheet processed by using the method wherein etching just like a complicated etching pattern is applied on a surface to be processed, formation of a vertical hole and execution of groove processing are simplified, and several hundreds etching depth μm can be attained.

CONSTITUTION: The surface to be processed of a work 1 is covered with a mask 2 on which a given pattern is formed. Either the work or an injection nozzle 4 is fixed, and the other of the injection nozzle and the work is swung in the direction of the short side of a rectangular injection nozzle 5. By increasing the size of the rectangular injection nozzle to a value higher than the size of the surface to be processed of the work, a sold gas two-phase flow is injected at a high speed from a position above the mask to apply surface processing on the surface to be processed of the work.