appropriate advance angle during the operation the barrel structure 3 is disposed on a machine pedestal 1 below such that the barrel 3 is vibratably supported by a pluralily of springs 2 2 mounted between the barrel and pedestal the barrel 3 includes two parallel barrel sections 3c and 3d running in a longitudinal direction and two semicircle barrel sections 3a and 3d traversing the barrel sections 3c and 3d on the opposite ends thereof those barrel sections being connected to constitute an annular barrel the aforementioned motor 5 is electrically connected via a variable frequency inverter 8a to a commercial frequency power supply 7 the aforementioned motor 6 is connected to a variable frequency inverter 8b which supplies a variable frequency to drive the motor for rotation with angular velocities controlled by the inverter 8b the rotary shaft 9 of the motor 5 has a pair of unbalancing weights 10 and 11 respectively mounted on the upper and lower ends thereof and the rotary shaft 9a of the subsidiary motor 6 has a pair of unbalancing weights 10a and 11a respectively mounted on the upper and lower ends thereof the rotational speed of both motors are the same in stationary working when the advance angle of both unbalancing weights is set for predetermined value when the advance angle is not the predetermined.