A charged particle beam device capable of generating an image having uniform image quality in a field of view is provided. The charged particle beam device includes: a beam source configured to irradiate a sample with a charged particle beam; a diaphragm including an opening used for angle discrimination of secondary charged particles emitted from the sample; a first detector provided closer to the sample than the diaphragm, and configured to detect a part of the secondary charged particles; a second detector provided closer to the beam source than the diaphragm, and configured to detect secondary charged particles passing through the opening; an image generation unit configured to generate an image based on a first signal output from the first detector or a second signal output from the second detector; and a composite ratio calculation unit configured to calculate a composite ratio for each position in a field of view based on the first signal or the second signal with respect to a calibration sample that is a sample having a flat surface. The image generation unit generates a composite image by synthesizing the first signal and the second signal with respect to an observation sample using the composite ratio.