The present invention provides a particle beam therapy apparatus and an operating method thereof. When the energy of the particle beam being emitted from the accelerator (1) is set for each slice group (F) containing two or more adjacent slices (S), and the amount of attenuation is set for each slice (S) in the slice group (F), for each slice group (F), the value of the energy being emitted from the accelerator (1) is set to be higher than the value of the energy being corresponding to the slice (S) at the deepest position such that a transmissive plate could have a predetermined thickness with respect to the slice (S) being at the deepest position among the slice group (F), and with regard to the thickness of transmissive plate set for each slice group (F), the thickness being set for the slice group (F) at the deep position is thicker than or equal to the thickness being set for the slice group (F) at the shallow position, and the thickness being set for the slice group (F) at the deepest position is thicker than the thickness being set for the slice group (F) at the most shallow position.在依各個包含相鄰接的兩個以上切片(S)之切片群(F)設定從加速器(1)射出之粒子線的能量，且依該切片群(F)內的各切片(S)設定衰減量之際，依各個切片群(F)，以針對該切片群(F)內位置最深的切片(S)，穿透板會具有預定的厚度之方式，將從加速器(1)射出之能量設定為比位置最深的切片(S)所對應之能量高之值，並且依各個切片群(F)而設定之穿透板的厚度，係針對位置深的切片群(F)而設定之厚度大於等於針對位置淺的切片群(F)而設定之厚度，且針對位置最深的切片群(F)而設定之厚度比針對位置最淺的切片群(F)而設定之厚度厚。
