A charged particle beam treatment apparatus includes an irradiator that irradiates an irradiation target with a charged particle beam by a scanning method, in which the irradiator includes a scanning electromagnet that performs scanning with the charged particle beam, is rotatable around the irradiation target by a rotating gantry, and emits the charged particle beam with a base axis orthogonal to a center line of the rotating gantry and passing through the center line as a reference, and when the scanning electromagnet is not operated, the charged particle beam which is emitted from a tip portion of the irradiator is inclined in one direction with respect to the base axis.