A radiation source is moved, relative to a detection means, in a movement range that is calculated based on a desired slice angle with respect to a predetermined base point on a base plane that defines a range of obtaining a slice image of a subject. The radiation source is moved to a plurality of positions, and a plurality of radiographic images of the subject corresponding to the plurality of positions are obtained by irradiating the subject with radiation from the plurality of positions. Further, a slice image of the subject is reconstructed from the plurality of radiographic images. When the slice image is reconstructed, radiographic images to be used to reconstruct the slice image are selected based on a distance from the detection surface of the detection means to a slice plane on which the slice image is to be generated, and the desired slice angle.