The present invention provides a charged particle beam apparatus that keeps the degree of vacuum in the vicinity of the electron source to ultra-high vacuum such as 10−8 to 10−9 Pa even in the state where electron beams are emitted using a non-evaporable getter pump and is not affected by dropout foreign particles.The present invention includes a vacuum vessel in which a charged particle source (electron source, ion source, etc.) is disposed and a non-evaporable getter pump disposed at a position that does not directly face electron beams and includes a structure that makes the non-evaporable getter pump upward with respect to a horizontal direction to drop out foreign particles into a bottom in a groove, so that the foreign particles dropped out from the non-evaporable getter pump do not face an electron optical system. Or, the present invention includes a structure that is covered by a shield means, or a means that is disposed immediately on a surface of the non-evaporable getter pump but at a position where the electron beams are not seen and has a concave structure capable of trapping the dropout foreign particles on a lower portion of the non-evaporable getter pump.