1. An image processing device for generating a display image on the basis of three-dimensional data, comprising: a reader for reading and storing three-dimensional data indicative of a structure of a virtual three-dimensional object constructed by a set of specific structures oriented in a predetermined direction into a predetermined storage; a projection plane setter for setting a directional relationship between a virtual plane of projection on which said virtual three-dimensional object is projected and said virtual three-dimensional object; a reference position setter for setting a reference position of a specific structure included in said set of specific structures; a basic image generator for generating a basic image by projecting said specific structure oriented in said predetermined direction onto said virtual plane of projection in accordance with said directional relationship and, also, recognizing a reference image position corresponding to said reference position in said basic image; a detector for detecting each of reference projection positions in which said reference position of each specific structure included in said set of specific structures is projected to said virtual plane of projection at a time of projecting said virtual three-dimensional object onto said virtual plane of projection; an adjusted image generator for generating adjusted basic images on the basis of said basic image by adjusting a positional relationship between said basic image and said virtual plane of projection in accordance with said each of reference projection positions detected by said detector; and a display image generator for generating a display image by combining said adjusted basic images to each other.