PURPOSE: To provide the image processor which can display not only an object but also a curvature of its surface and/or thickness of each part of the object on a three-dimensional image.

CONSTITUTION: Three-dimensional data 21 obtained by two-dimensional slice data becomes a three-dimensional image 23 by a three-dimensional image generating means 22. On the other hand, from the three-dimensional data 21, a curvature is calculated by a curvature calculating means 24, and its curvature is expressed by a curvature display means 25 by allowing it to correspond to the three-dimensional image 23, and displayed as a three-dimensional image 27 for displaying its curvature by a display device 26. The curvature is calculated with regard to a display area. Also, as for such dcsignation that in which display area the curvature is to be calculated is executed by a pointing device being a designating means. The curvature display means 25 can be constituted so that a curvature and a color, and equal curvature line, or a value of a calculated curvature are allowed to correspond to each other and displayed.