Smoothing processing appropriate for a subject is performed and a CT image in which artifacts are reduced is acquired. At least a part of the X-ray detecting data 171 and the projection data 174 is used to generate boundary data 175, and at least one of the X-ray detecting data and the projection data is subjected to smoothing processing, by using the boundary data as a threshold. With this configuration, it is possible to perform smoothing processing by using as the threshold, the boundary data generated from the X-ray detecting data that passed through the subject or its projection data, enabling the smoothing processing adapted to the subject, and accordingly, the artifacts are removed while suppressing deterioration of spatial resolution.
