Disclosed is a charged particle beam apparatus wherein a partitioning film capable of transmitting a charged particle beam is provided between a charged particle optical system and a sample, said charged particle beam apparatus eliminating a contact between the sample and the partitioning film even in the cases where the sample has recesses and protrusions. On the basis of detection signals or an image generated on the basis of the detection signals, a distance between a sample and a partitioning film is monitored, said detection signals being outputted from a detector that detects secondary charged particles discharged from the sample due to irradiation of a primary charged particle beam.