[Problem] To adjust astigmatism quickly with a simple algorithm by utilizing an autofocus estimation value of an image obtained from a pattern formed on a sample. [Means] A charged particle beam apparatus 300 for observing and estimating a sample W by applying a charged particle beam to sample W to detect secondary charged particles, such as electrons emitted from the sample, reflected electrons and backscattered electrons comprises astigmatism adjusting means 17 for adjusting astigmatism of the charged particle beam. Astigmatism adjusting means 17 is supplied with a correction voltage which maximizes a focus estimation value obtained from a pattern formed on sample W. Astigmatism adjusting means 17 is a multipole including a plurality of pairs of electrodes or coils facing each other to place the optical axis of the charged particle beam at the center. Also disclosed is a charged particle beam apparatus 400 capable of observation and estimation of a sample surface in a condition where no charge up exists over the whole sample W.