There is provided a charged particle beam system for reducing phase variations in a charged particle beam due to sixth order three-lobe aberration. The charged particle beam system (100) is equipped with an aberration corrector (30) for correcting aberrations in the optical system, and includes: an aberration measuring section (44) for measuring sixth order three-lobe aberration of sixth order geometric aberration, a computing section (46) for computing the magnitude of at least one of fourth order three-lobe aberration of fourth order geometric aberration and three-fold astigmatism of second order geometric aberration for reducing phase variations in the charged particle beam due to the sixth order three-lobe aberration on the basis of the measured sixth order three-lobe aberration, and a controller (48) for controlling the aberration corrector (30) to produce at least one of the fourth order three-lobe aberration and the three-fold astigmatism on the basis of the computed magnitude.