1. A method of constructing a three-dimensional image, comprising the steps of: obtaining a first series of tilted images which are constituted by electron microscope images or elemental mapping images of a sample at different tilt angles and which have been obtained by tilting the sample in a plurality of angular increments; rotating the sample through 180 degrees about an axis perpendicular to the surface of the sample after the step of obtaining the first series of tilted images; obtaining a second series of corresponding tilted images which are constituted by electron microscope images or elemental mapping images of the sample at different tilt angles; and constructing the three-dimensional image on the basis of the first and second series of tilted images wherein, during the step of constructing the three-dimensional image, said second series of tilted images is rotated to the same orientation as said first series of tilted images and some of the electron microscope images or elemental mapping images of the sample constituting the first series of tilted images are replaced by some of the electron microscope images or elemental mapping images of the sample constituting the second series of tilted images so as to create a third series of tilted images for constructing the three-dimensional image.