That is, the biasing forces of the torsion springs 8 and 13 by the hopper cam 9 and the parting cam 14 can variously be adjusted by elements such as the forms of the peripheral surfaces of the hopper and parting cams 9 and 14, the direction and angle of rotation thereof, the spring constants of the torsion springs 8 and 13, gear ratios of the gears 216 a to 216 c, etc.