A charged particle beam therapy apparatus includes an accelerator accelerating a charged particle and emitting a charged particle beam, an irradiation unit irradiating an irradiation subject with the charged particle beam, and a ridge filter provided in the irradiation unit and generating a spread out Bragg peak of the charged particle beam. The ridge filter includes multiple damping members reducing energy of the incident charged particle beam, in an intersecting direction intersecting an irradiating direction of the charged particle beam. The damping member has a cross-sectional area changing along the irradiating direction and has a side surface of when being seen in the intersecting direction, being bonded to a side surface of another damping member. A pass-through portion passing through the ridge filter in the irradiating direction is formed at a position different from a position of the damping member of when being seen in the irradiating direction.