To provide a radiation therapeutic apparatus in which a marking on the surface of the body of a patient being necessary for positioning the patient to the range of irradiation of radiation can be wiped out and mental pain and unconvenience on life of the patient can be solved.

An image corresponding to the range of irradiation of radiation by a radiation irradiating means 2 is projected on the surface of the body of a patient supported by a supporting member 4. The supporting member 4 is relatively moved to the radiation irradiating means in such a way that the position of the projected image coincides with the position of the target range of irradiation of the radiation on the surface of the body of the patient 3. When both positions coincide with each other, image data corresponding to a definite site of the patient 3 are formed and stored. Based on the image data, an image corresponding to the definite site of the patient 3 is projected on the surface of the body of the patient 3 supported. The supporting member is relatively moved to the radiation irradiating means so as to make the position of the projected image coincide with the actual definite site of the patient.