Charged Particle Beam Apparatus and Focus Adjusting Method Therefor

A technique that enables automatic focus adjustment even for a sample having regions with different heights is proposed. A charged particle beam device according to the disclosure includes: a sample holder configured to hold a sample; a sample stage configured to move the sample; a charged particle gun and a charged particle beam column configured to irradiate the sample with a charged particle beam; an objective lens configured to perform focus adjustment by changing an intensity of a focusing effect on the charged particle beam; a detector configured to detect electrons from the sample and output a signal forming an electron image; an optical imaging device configured to capture an optical image of the sample; and a control device configured to calculate height information of the sample based on the optical image obtained by imaging the sample by the optical imaging device, and automatically set a focus adjustment value of an observation site based on the height information (see FIG. 5).