PURPOSE: To manufacture a synthetic resin-made three-dimentional impeller, by composing the forming mold of a blade disk having three-dimensional curve of a movable mold and a residual mold and making a residual mold separable from the movable mold for the intricate inner part of a three-dimensional blade.

CONSTITUTION: 4, 4' are forming molds, the former constitutes a face mold and the latter a back mold. 5 is a residual mold which is attached freely detachably to the face side movable mold forming a three-dimensional blade and said residual mold 5 is jointed to the face side movable mold 4 by engagement means of a dovetail tenon 6a and a mortise 6b. When synthetic resin liquid 7 is forced in and molding is finished, the back side movable 4' is drawn to (A) direction, meanwhile the face side movable mold 4 is drawn to (B) direction, leaving the residual mold 5 separated. Then, said residual mold 5 is drawn to an arrow mark (C) direction and taken out. A synthetic resin-made three-dimensional impeller can be obtained in such a way.