Particle beam irradiation device

The invention provides a particle beam irradiation device capable of reducing expansion of a particle beam emitted from an accelerator in a transport path with high precision. The second shield member (44B) is disposed apart from the first shield member (44A) toward the downstream side in the travel direction (D1). Therefore, a particle beam (B) having a large angle with respect to the base axis (AX) among the particle beams (B) passing through the opening (50A) of the first shield member (44A) can be shielded by the second shield member (44B) at a position separated on the downstream side in the direction of travel (D1). Furthermore, when the opening (50A) of the first shield member (44A) is viewed from the upstream side in the travel direction (D1), the opening (50B) of the second shield member (44B) is visible from the downstream side. Therefore, among the particle beams (B) passing through the opening (50A) of the first shield member (44A), the particle beam (B) having a small angle with respect to the ba