1. An image processing apparatus comprising: a correlating unit configured to acquire correlation information that correlates a first three-dimensional image of a target object with a second three-dimensional image of the target object; and a corresponding cross-sectional image generation unit configured to generate a corresponding cross-sectional image of one of the first three-dimensional image and the second three-dimensional image, if a cross section is set on the other of the first three-dimensional image and the second three-dimensional image, based on the correlation information.