1. An image processing device comprising: a processor configured by one or more programs of executable instructions stored in a non-transitory medium, to comprise an extraction unit extracting a vertebral region from a series of tomographic images in which at least a part of a spine of a subject was scanned, a calculation unit calculating a length in an anteroposterior direction of the subject, for each cross section in the vertebral region extracted by the extraction unit, a cross-section identifying unit identifying a cross section including a spinous process if the length in the anteroposterior direction of-the subject in the vertebral region calculated by the calculation unit is larger than a predetermined reference value, and a spinal canal stenosis evaluation unit evaluating a spinal canal stenosis by specifying a cross-sectional position of the cross-section identified by the cross-section identifying unit as a site to be analyzed; and a display unit displaying evaluation results by the spinal canal stenosis evaluation unit, wherein the spinal canal stenosis evaluation unit evaluates an asymmetry of a spinal canal shape in the cross section to be analyzed, as an evaluation index of the stenosis.