PURPOSE: To reduce the number of required support means by supplying a new material to a base member to successively augment the base member and thereby forming at least a portion of a part and supplying the new material to the base member so that a construction force is resisted by the axial tension of the new material. CONSTITUTION: When a part 10 is formed based on a computer assisted design model using a fluid material suited for bridging, first a new material is supplied to a base member and thereby the base member is successively augmented to form at least a portion of the part 10. Next, the new material is supplied to the base member according to a specified design so that a construction force is resisted by axial tension in the newly supplied material. For example, the part 10 has a non-supported part 12 or an overhang 14 not supported from beneath. A bridge long enough to cover a bridging distance 28 is formed by extruding the new material 22 from the base member 24 to bridge a nozzle 26. Thus the number of required support means is reduced.