To provide a charged particle beam treatment device capable of suppressing an increase in a beam size while suppressing a decrease in a beam current of a charged particle beam.SOLUTION: A charged particle beam treatment device 1 includes: an accelerator 3 for accelerating a charged particle and emitting a charged particle beam B； an attenuation part 21 for lowering energy of the charged particle beam B by making the charged particle beam B emitted from the accelerator 3 incident； a magnetic field generation part 22 for generating a magnetic field H having a component in the same direction as an emission direction of the charged particle beam B in the attenuation part 21； and an irradiation part 2 for irradiating the charged particle beam B passing through the magnetic field generation part 22 onto a tumor (an irradiated body) 14.SELECTED DRAWING: Figure 5【課題】荷電粒子線のビーム電流の低下を抑制しつつ、ビームサイズの拡大を抑制することが可能な荷電粒子線治療装置を提供する。【解決手段】荷電粒子線治療装置１は、荷電粒子を加速して荷電粒子線Ｂを出射する加速器３と、加速器３から出射された荷電粒子線Ｂを入射させることで、当該荷電粒子線Ｂのエネルギーを低下させる減衰部２１と、減衰部２１において、荷電粒子線Ｂの出射方向と同方向の成分を持つ磁場Ｈを発生させる磁場発生部２２と、磁場発生部２２を通過した荷電粒子線Ｂを腫瘍（被照射体）１４に照射する照射部２と、を備える。【選択図】図５
