A charged particle beam apparatus includes a charged particle source which generates a charged particle beam, a condenser lens which converges the charged particle beam, a deflector which deflects the charged particle beam to scan a sample with the charged particle beam, an objective lens which converges the charged particle beam on the surface of the sample, a sample position imaginary variation detection part which detects an imaginary variation of a sample position caused by variation of the focal position of the charged particle beam due to variation in the potential of the sample, and a sample position imaginary variation compensation part which compensates for the detected imaginary variation of the sample position.