The present invention considers the influence on the dose distribution by errors relative to the irradiation based on the therapy planning information stored in the therapy planning information storing part 11 by the dose errors distribution computing part 13 corresponding to at least one of the information of errors of spot position, energy and beam irradiation amount occurred by operational error of machine and moving of irradiation target comprised in the particle beam therapy apparatus, and computes the distribution of the dose errors, wherein the information of errors is stored in the errors information store part 12. Accordingly, time for measuring is shortened without lowering the measuring accuracy of the dose distribution.藉由線量誤差分布演算部13，對於依據治療計畫資訊記憶部11所記憶之治療計畫資訊之照射，因應誤差資訊記憶部12所記憶之由於粒子射線治療裝置所包含之機器的動作誤差、照射對象的動作所產生之點位置、能量、射束照射量之中至少一者之誤差的資訊，考慮誤差對線量分布造成之影響而演算線量誤差的分布，藉此可不使線量分布的測量精確度下降而謀求縮短測量時間。
