It is an object of the present invention to obtain an image which is focused on all portions of a sample and to provide a charged particle beam apparatus capable of obtaining a two-dimensional image which has no blurred part over an entire sample. In order to achieve the above object, the present invention comprises means for changing a focus condition of a charged particle beam emitted from a charged particle source, a charged particle detector for detecting charged particles irradiated from a surface portion of said sample in response to the emitted charged particle beam, and means for composing a two-dimensional image of the surface portion of the based on signals on which said charged particle beam is focused, said signals being among signals output from the charged particle detector.