The present invention provides a laser processing apparatus having a laser oscillator for outputting a pulsed laser beam; deflection unit for deflecting the pulsed laser beam to irradiate a object to be processed with the deflected pulsed laser beam; a mounting base on which the object is placed and which is movable in an axial direction or two-axial directions perpendicular to each other; and local shielding unit for controlling an atmosphere around the surface of the object to be processed which is irradiated with the laser beam. When a thin semiconductor film with a thickness of 1 .mu.m or less is formed over the surface, minute convex portions are formed, which causes a problem that characteristics of TFTs vary among elements. Minute particles generated and adhered to a main surface of a substrate through a laser processing, which is difficult to remove in general surface cleaning, become preventable by the invention.