Abstract: A folding fan, more specifically a folding fan used as an advertisement medium. A rectangular shape piece of paper is placed on another paper piece of the same shape, the pieces of paper are opened in such a way that the vertex A at the top right side of one rectangular paper piece is against the center of an opening m selected at a prescribed position on the center line F in the direction of a longer side agrees with the vertex C at the top left side of another rectangular paper piece. The line segment connecting the point E, which is obtained on the vertex side at the bottom right side of the rectangular paper piece at the point where the distance between the vertexes B and D on the bottom side of the two paper pieces opposing the agreed vertex is divided into three equal parts. The agreed vertex A at the top right side of the rectangular paper piece is taken as a bend line, and the rectangular paper piece is folded in the shape of a valley at the bend line.