In a control apparatus for a radiotherapy apparatus, each of a plurality of separation results indicates an objective portion template and a non-objective portion template. The separation result is calculated such that a difference between a first template production image and an image produced by superimposing an objective portion template in a position of a designated region on the non-objective portion template is small and a difference between the second template production image and an image produced by superimposing the objective portion template in a position of an assumption region, which is different from the designated region, on the non-objective portion template is small.
