PURPOSE: To shorten the processing time, and to execute a display at a high speed, at the time of making three-dimensional image data subjected to stereoscopic vision display, based on a rotational display method.

CONSTITUTION: A CPU operates a coordinate obtained by rotating voxel data of the (x)-(z) face at the time when the (y) axis of three-dimensional image data is a rotation axis, by θ degrees (0≤θ≤180°) (step 23). In that case, an initial value determined by the angle θ is set, and by cumulative addition from this initial value, the coordinate of the voxel data of its face is rotated. In each rotational position, a parameter is changed in order of (z), (x) and (y) and projected in the (z) axis (rotation axis) direction, and shading is executed by a (z) buffer algorithm. In that case, by taking notice of a fact that as for the projecting directions of θ degrees, and θ+180 degrees, the lines are the same and the directions are opposite to each other, the projection at the time of θ+180 degrees is also executed together at the time of projection at the time of θ degrees (step 24-34). Subsequently, by changing the rotation angle by 11.25 degrees each, the abovementioned processings are executed (steps 35, 36).