An object of the present invention is related to detecting of a detection signal at an optimum position in such a case that a sample plane is inclined with respect to a charged particle beam.The present invention is related to a charged particle beam apparatus for irradiating a charged particle beam to a sample, in which a detector is moved to a plurality of desirable positions around the sample so as to optimize positions of the detector. In accordance with the present invention, since it is possible to obtain an optimum detection signal in response to an attitude and a shape of the sample, a highly accurate sample observation, for instance, an SEM observation, an STEM observation, and an FIB observation can be carried out. Moreover, in an FIB-SEM apparatus, it is possible to highly accurately detect an end point of an FIB process.