PURPOSE: To adjust the focusing position of the electron beam of the part to be machined to perform machining evenly and improve performance by providing a position adjusting means to the focusing means of charged particle beams.

CONSTITUTION: After the work 5 is positioned on a stage 4, the specified vacuum state is maintained by the exhaust device connected to the opening part 101 of a vacuum chamber 1. Thereafter, a focusing means 8 is adjusted approximately right under an electron beam generator 6 by an adjusting means 12. Next, the position of the focusing means 8 is so adjusted that the electron beam 7 generated radiates the machining part. Then, while the moving table 3 and work 5 are being moved in the direction of X1 or X2, machining is accomplished. If at this time, the surface of the work 5 is not even and has a serration t, then the focusing means 8 is lowered by the height corresponding to the height t by an adjusting mechanism 121. If the adjusting means 12 is made adjustable with respect to the X-axis, Y-axis, Z-axis, then fine adjustment may be accomplished.