A radio-therapy apparatus includes a radiation head configured to irradiate a therapeutic radiation, and an image processing section configured to generate an image of a diseased portion of a specimen from a result of detection of the diseased portion while tracking the diseased portion to which the therapeutic radiation is irradiated from the radiation head. A control section controls the radiation head and the image processing section such that a period containing the generation of the image and the irradiation of the therapeutic radiation is repeated and the detection of the diseased portion in a next period is started prior to an end of a current period. A recording section records the image of the diseased portion generated by the image processing section in order.