The radiation therapy system of the present invention includes: a proton beam generating device 103; a rotary irradiation device 105 that irradiates a proton beam generated by the proton beam generating device 103 toward a target 201 in an irradiated body 111; a control device 102a that applies a proton beam The generator 103 and the rotary irradiation device 105 perform control; a converter 303 is provided on the object 111 to be irradiated; and a signal processing device 302 determines whether or not a sound wave is generated from the reference mark 101 based on a signal waveform measured by the converter 303. This determines whether the proton beam is irradiated at the planned location.本發明之放射線治療系統具備:質子束產生裝置103;旋轉式照射裝置105,其將由質子束產生裝置103產生之質子束朝向被照射體111中之靶201照射;控制裝置102a,其對質子束產生裝置103及旋轉式照射裝置105進行控制;轉換器303,其設置於被照射體111;及信號處理裝置302,其基於由轉換器303測定之信號波形,判定有無自基準標記101產生音波,藉此判定質子束是否照射於計劃之位置。