In a SEM device which enables observations under an atmospheric pressure, in the event that a diaphragm is damaged during an observation of a sample, air flows into a charged particle optical barrel from the vicinity of the sample, due to the differential pressure between the inside of the charged particle optical barrel under vacuum and the vicinity of the sample under the atmospheric pressure. At this time, the sample may be sucked into the charged particle optical barrel. In this case, a charged particle optical system and a detector are contaminated thereby, which causes performance degradation or failures of the charged particle microscope. For coping therewith, it is necessary to prevent the charged particle optical barrel from being contaminated, without inducing a time lag, with a simple structure. In a charged particle beam device adapted to place a sample in a non-vacuum environment, there is provided a filter member which is placed on the path of a primary charged particle beam at least in a state where the primary charged particle beam is directed to the sample and, further, is adapted to transmit or pass, therethrough, the primary charged particle beam and secondary charged particles derived from the sample, while intercepting at least a portion of a scattering substance which is scattered in the event of a fracture of the diaphragm.