An x-ray CT image processing method which carries out a statistical estimate in prior knowledge relating to the movement and the x-ray absorption coefficient of a measurement subject comprises: a step of hypothesizing that the measurement subject changes smoothly over time, and defining a first probability model (prior knowledge of the measurement subject over all times) relating to movement and a second probability model (projected image observation model over all times) relating to observation and a step of carrying out a statistical estimate dependent on both the first probability model and the second probability model. The first probability model relating to the movement of the measurement subject and the second model relating to observation are defined as probability models with which statistical estimates are carried out at the outset, and motion and CT images are simultaneously estimated by carrying out induction based on the probability models.
