To easily grasp the moving direction of the visual point of an organ such as a blood vessel by giving pixel value information of an original picture to a curved surface passing through plural visual points and shading the given curved surface so as to form and display a picture.

Plural visual points 5a to 5g are set inside of a blood vessel 12 as an observing object included in a three-dimensional original picture 10 by a center projecting method. Then, a curved surface passing through the plural visual points 5a to 5g is set and pixel value information of the picture 10 is given to the curved surface to synthesize a three-dimensional picture obtained by shad-projecting the given curved surface to a prescribed projecting surface and a cross-section image cut off at an angle by a guide image 6 to form a picture 4, which is displayed on a CRT monitor 1. Thus, it is possible to easily grasp the displaying position of an organ such as the blood vessel 12 or an internal organ or the moving direction of the visual point from there.