To provide a particle beam irradiation system by a scanning irradiation method, capable of forming a radiation dose distribution as planned, and allowing for shortening of an irradiation time compared to a conventional method.SOLUTION: The particle beam irradiation system comprises: target monitoring devices 35,36 measuring a position of a target 26； and a control system 7. The control system 7 performs: such a tracking irradiation that an exciting current value of scanning electromagnets 31,32 is corrected on the basis of a signal from the target monitoring devices； and such a gate irradiation that depth of the target 26 is calculated on the basis of a signal from the target monitoring devices, and the target 26 is irradiated with charged particle beams when the depth of the target 26 is in a previously set depth permission range. The control system 7 performs the tracking irradiation when the depth of the target 26 measured by the target monitoring devices falls within in a depth permission range.SELECTED DRAWING: Figure 1【課題】計画通りの線量分布を形成することができ、かつ従来の手法に比べて照射時間を短縮することが可能な、スキャニング照射法による粒子線照射システムを提供する。【解決手段】標的２６の位置を計測する標的監視装置３５，３６と、標的監視装置からの信号に基づき走査電磁石３１，３２の励磁電流値を補正して荷電粒子ビームを標的２６に照射する追尾照射、および標的監視装置からの信号に基づき標的２６の深さを演算し、標的２６の深さが予め定めた深さ許可範囲内にあるとき荷電粒子ビームを照射するゲート照射を行う制御システム７と、を備え、制御システム７は、標的監視装置によって計測した標的２６の深さが深さ許可範囲内にあるときに追尾照射を行う。【選択図】図１
