A charged particle beam irradiation apparatus according to an embodiment includes: a first scanning electromagnet device configured to deflect a charged particle beam to a second direction that is substantially perpendicular to a first direction along which the charged particle beam enters, the first scanning electromagnet device having an aperture on an outlet side larger than that on an inlet side； and a second scanning electromagnet device configured to deflect the charged particle beam to a third direction that is substantially perpendicular to the first direction and the second direction, the second scanning electromagnet device having an aperture on an outlet side larger than that on an inlet side, the first scanning electromagnet device and the second scanning electromagnet device being disposed to be parallel with the first direction.
