To relatively inexpensively provide the entire part of an aperture by building a constitution capable of reducing the size and weight of a rotary gantry while effectively utilizing the advantages of 360° irradiation.

The cancer treatment apparatus (accelerator irradiation apparatus for radio-therapy) has a beam line 5 for receiving the positive beam PB from an accelerator AC and the rotary gantry 2 mounted with this beam line 5. The beam line 5 has a deflecting electromagnet 7b for deflecting the positive beam PB from the accelerator side toward the patient P side and an irradiation field forming device 9 for forming the irradiation field of the beam PB via this deflecting electromagnet 7b according to the treating part of the patient P. The rotary gantry 5 has rotating means (a frame 4 for rotation and rotating mechanisms 6 (a projecting body 10 and a guide 11)) for spatially rotating the beam line 5 including the deflecting electromagnet 7b and the irradiation field forming device 9 to the irradiation position in a radial direction having a rotating angle of about 90° around the patient P.