A laser beam machining method for a printed circuit board, for enabling to bring the depth of a bottom surface of grooves within an overlap region, which is irradiated with a laser beam, repetitively, to be nearly equal to that of the bottom surface of grooves within other regions, comprises the following steps of: fixing a line beam 4, which is shaped into a rectangular having a length sufficiently larger than its width, in a cross-section perpendicular to a central axis thereof; executing a belt-like machining on a certain region of the printed circuit board 6, while moving a mask 1 and the printed circuit board 6 in opposite directions, in a direction of the width of the line beam 4 (i.e., X-direction); and thereafter moving the mask 1 and the printed circuit board 6, relatively, into a direction perpendicular to the belt-like machining direction, and repeating the belt-like machining upon other region, newly, thereby machining a groove on the printed circuit board 6, wherein when repeating the machining overlapping the regions, the machining is conducted with using the line beam 4 being shaped to be oblique on its overlapping side, to be overlapped on that region.