1. An image processing device comprising: an extraction unit extracting a vertebral region from a series of tomographic images in which at least a part of the spine was scanned, a calculation unit calculating a length in the anteroposterior direction of an object 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 an object in the vertebral region calculated by the calculation unit is larger than a predetermined reference value, a spinal canal stenosis evaluation unit evaluating the spinal canal stenosis by specifying a cross-sectional position 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.