To provide a charged particle beam optical system capable of reducing the required number of driving power supplies while mitigating the requirement on the stability and settling time of the power supplies for lenses and deflectors.

This charged particle beam optical system projects a patterned charged particle beam through a mask 1 receiving charged particle beam illumination to a wafer 7 with lenses 2, 5 of two stages and multiple deflectors 8, 10 to form an image. Most of multiple aberration correcting deflectors 10, 12 have combination coils constituted of main coils 10a, 12a having a large ampere-turn and auxiliary coils 10b, 12b having a small ampere-turn. The main coils 10 a, 12 a of the deflectors 10, 12 are driven by the same power supply 24.