PURPOSE: To form a uniform spiral shape by providing a 1st mounting plate supported to a 1st supporting axis, a 2nd mounting plate supported to a 2nd supporting axis and a fixing means mounted on one side of these 1st and 2nd mounting plates and clamping the neighborhood of a slit on an annular original plate.

CONSTITUTION: A movable body 6 is moved by an operating means and the 2nd mounted plate 27 supported on the movable body is faced to the 1st mounting plate 25 supported on a base 4 and approached to it. The slit part 2a of the annular original plate 2c is clamped respectively to the fixing means 29,30 mounted on the 1st and 2nd mounting plates. The operating means is operated to move the movable body and when the 2nd mounting plate is separated a prescribed amount from the 1st mounting plate, the annular original plate is expanded from the slit part to the axial direction to form a spiral shape, therefore, an eccentricity L is generated between the 1st supporting axis 16 projected on the base and 2nd supporting axis 21 projected on the movable body and a spiral auger blade generates a twisting force to the inside. Since the 1st and 2nd mounting plates turn smoothly with the twisting force of the auger blade, the precise auger blade can be formed.