A charged particle beam device enabling prevention of degradation of reproducibility of measurement caused by an increase of the beam diameter attributed to an image shift and having a function of dealing with device-to-device variation. The charged particle beam device is used for measuring the dimensions of a pattern on a specimen using a line profile obtained by detecting secondary charged particles emitted from the specimen when the specimen is scanned with a primary charged particle beam converged on the specimen. A lookup table in which the position of image shift and the variation of the beam diameter are associated is prepared in advance by actual measurement or calculation and registered. When the dimensions are measured, image processing is carried out so as to correct the line profile for the variation of the beam diameter while the lookup table is referenced, and thereby the situation where the beam diameter is effectively equal is produced irrespective of the position of the image shift. Whit this, measurement by the charged particle beam excellent reproducibility can be carried out.