An objective of this invention is irradiating an irradiation object with a small beam size even when the charged particle beam has a low energy.A particle ray irradiation apparatus (58) of this invention includes a vacuum duct (6, 7) forming a vacuum area through which a charged particle beam (1) passes, a non-metal vacuum window (8) allowing the charged particle beam (1) to be released from the vacuum area, a scanning electromagnet (2, 3) scanning the charged particle beam (1) in a direction perpendicular to a beam axis, a monitor device (67) having a position monitor (5) detecting the passing position and the beam size of the charged particle beam (1), a low scattering gas filled chamber (39) covering the vacuum window (8) with the motor device (67) being disposed at a downstream side thereof, and an irradiation management device (20) controlling irradiation of the charged particle beam (1). The relative positions of the motor device (67) and the vacuum window (8) in the beam axis direction can be changed to desired positions, such that the low scattering gas filled chamber (39) is filled with a low scattering gas having a scattering degree lower than air when the charged particle beam (1) is irradiated.本發明之目的在於提供一種粒子線照射裝置及粒子線治療裝置，其即便荷電粒子束為低能量亦可以較小之射束尺寸照射於照射對象。本發明之粒子線照射裝置(58)，其特徵為具備：真空導管(6、7)，形成供荷電粒子束(1)通過之真空區域；非金屬之真空窗(8)，可供荷電粒子束(1)從真空區域釋出；掃描電磁鐵(2、3)，將荷電粒子束(1)朝向與射束軸呈垂直之方向掃描；監視裝置(67)，具有檢測荷電粒子束(1)之通過位置及射束尺寸的位置監視器(5)；低散亂氣體填充室(39)，覆蓋真空窗(8)且於下游側配置有監視裝置(67)；以及照射管理裝置(20)，控制荷電粒子束(1)之照射，且低散亂氣體填充室(39)，係使監視裝置(67)與真空窗(8)之位於射束軸方向的相對位置能夠變更地配置在所期望之位置，且填充有於荷電粒子束(1)被照射時散亂比空氣小的低散亂氣體。
