To provide an air sanding machine capable of highly efficiently and accurately grinding a spot-welded weld protrusion and a convex part.

An eccentric shaft 6 is directly coupled to the lower end of s rotor shaft 2a of an air motor 2. The central part of a circular polishing pad 5 is integrally fixed on the eccentric shaft 6 not through a bearing, rotation of the air motor 2 is transmitted directly to the circular polishing pad 5, and the circular polishing pad 5 is rotated at a high speed as it is caused to effect revolution movement. With the circular polishing pad 5 inclined obliquely downward toward a front, its front edge part is brought into a touch with a substance A to be ground, such as a weld protrusion, as it is moved in a longitudinal direction at intervals of a very short time, and the substance A to be ground is intermittently ground.