According to the invention, techniques for automatically adjusting for astigmatism in a charged particle beam apparatus. Embodiments according to the present invention can provide a charged particle beam apparatus and an automatic astigmatism adjustment methods capable of automatically correcting astigmatism and a focal point in a relatively short period of time by finding a plurality of astigmatism correction quantities and a focal point correction quantity in a single operation from a relatively small number of 2 dimensional images. Specific embodiments can perform such automatic focusing while minimizing damages inflicted on subject samples. Embodiments include, among others, a charged particle optical system for carrying out an inspection, a measurement and a fabrication with a relatively high degree of accuracy by using a charged particle beam.