1. A radiography apparatus comprising: a radiation source that outputs radiation to a subject; a detection means that detects the radiation that has passed through the subject; a body thickness information obtainment means that obtains body thickness information about the subject; a condition setting means that sets, based on the body thickness information, a slice image obtainment condition representing a range in which a slice image is obtained in the subject; and a slice image obtainment means that obtains, based on the slice image obtainment condition, the slice image.