To improve detection efficiency of secondary particles without increasing a size of a charged particle beam apparatus, a charged particle beam apparatus according to the invention includes: a charged particle beam source configured to irradiate a sample with a primary particle beam; a scanning deflector configured to scan and deflect the primary particle beam to a desired position of the sample; and a detector configured to detect secondary particles emitted from the desired position. The charged particle beam apparatus further includes: a focusing lens electrode arranged coaxially with the primary particle beam and configured to generate a focusing electric field that is an electric field that focuses a trajectory of the secondary particles; and a mesh electrode configured to reduce leakage of the focusing electric field on a trajectory of the primary particle beam.