A radiation emission control method, apparatus and the program capable of detecting respiratory phases of a test subject with constant accuracy and emitting radiation rays to the test subject in synchronization with an intended respiratory phase, while minimizing the radiation exposure to the subject. A test subject having a contour that varies with the respiration is optically imaged continuously by the optical image obtaining section to sequentially obtain optical images of the subject, and respiratory phases of the subject are detected simultaneously with the optical imaging by the respiratory phase detecting section based on the contour of the subject on the optical images. During the optical imaging, a radiation source is controlled by the control section such that radiation rays are emitted to the test subject when the detected respiratory phase corresponds to an intended respiratory phase of the subject.