An image processing apparatus and method produce sectional image data of a specimen in an arbitrary direction without deterioration of picture quality. A re-construction process produces volume data such that one of coordinate axes of a volume coordinate system such as the z axis is aligned with the principal axis of inertia of a specimen. When sectional image data of the specimen on a certain section are to be produced, from among all voxels which compose the volume data, those voxels whose z coordinates have predetermined values are read out, and the read out voxels are regarded as pixels. As a result, it is not necessary to interpolate pixels, and the deterioration of picture quality arising from interpolation of pixels is prevented.