1. An image processing apparatus, comprising: mapping image generating means, for generating a mapping image that represents a portion of a subject, by employing a first voxel data set, which is a voxel data set of a three dimensional image that represents the subject with at least a degree of opacity designated to each pixel thereof; aspect image generating means, for generating an aspect image that represents the aspect of a target which includes at least a portion of the subject from a second voxel data set of the three dimensional image that represents the subject; and image generating means, for generating a pseudo three dimensional image, by matching each position within the mapping image and the aspect image and executing volume rendering based on the degrees of opacity within the mapping image.