Aberration corrector and electron microscope

An aberration corrector, comprising:

• a first multipole and a second multipole configured to form a hexapole field;
• and
• a transfer optics including a plurality of round lenses, wherein
• the transfer optics
• is disposed between the first multipole and the second multipole,
• the first multipole and the second multipole have a relationship such that a three-fold symmetric astigmatism is cancelled in the same direction or is strengthened in the same direction by their combined action,
• the transfer optics provides a first action to a charged particle beam passing through the first multipole,
• the first action acts on a charged particle beam such that an absolute value of a slope of the charged particle beam passing through the first multipole is different from an absolute value of a slope of the charged particle beam passing through the second multipole, and
• the first action is performed by the function of the round lenses included in the transfer optics and is performed by adjusting at least one of focal lengths and positions of the plurality of round lenses.