1. An image processor, comprising: a storage that stores the volume data of a medical image including a chest of an examined body; a unit configured to specify a range including the heart based upon detecting an air region corresponding to the lungs in a tomographic image acquired based upon the volume data and extracting the detected air region from the acquired tomographic image so as to specify a cardiac search range; a unit configured to detect a ventricular region within the specified cardiac search range and to detect a left ventricular cluster and a right ventricular cluster based on specifying a circular contour of the left ventricular cluster and a crescent contour of the right ventricular cluster; a unit configured to detect the long axis of the ventricle in the detected ventricular region by acquiring a center of gravity of plural ventricle clusters from plural tomographic images to approximate an ellipsoid, the long axis of the ellipsoid being detected as the long axis of the ventricle; a unit configured to generate plural sectional images perpendicular to the detected ventricular long axis based upon the volume data; a unit configured to detect the inner wall and the outer wall of the ventricle from each of the plural sectional images; and a unit configured to analyze the ventricle based upon the detected ventricular inner wall and the outer wall.