PURPOSE: To simplify structure and to make sure action by supporting a moving knife rockingly based on a stationary knife of shear type by a shaft and driving a rotor attached to the shaft in a specific state by an exciting coil and a control part thereof.

CONSTITUTION: A moving knife 3 is arranged rockinly based on a stationary knife 2 of shear type in a casing 6 and freely displaced through a shaft 7 in the direction of center line. A control part sends a suitable electric current to an exciting coil in both directions, a rotor 10 is driven near by the exciting coil, the moving knife is properly brought into contact with the stationary knife and the rotor is provided with revolving force in reciprocating direction. The rotor is made of permanent magnet and the rotor is attached to the shaft in a state wherein the center of magnetic force action of the rotor is displaced in the direction opposite to action direction of contact force based on the center of magnetic flux of the exciting coil.