PURPOSE: To grind a cord-like useless work continuously without cutting it and ensure that a chain rail does not become bent due to the tension of the unused work.

CONSTITUTION: An useless work 2 is discharged from the chain rail 1 of a vacuum molder. This useless work 2 is ground using a grinding device 4. A guide table 3 receives the slack of the useless work 2 discharged from the chain rail 1. The useless work 2 discharged from the chain rail is drawn into the grinding device 4 by drive of a tension roller 6a and another torque motor 7. The tension state of the useless work 2 between the chain rail 1 and the tension roller 6a or the other component is detected using multi-axial photoelectric tubes 12, 13. Further, a control device 14 controls the drive of a torque motor 7 based on a detection signal from the multi-axial photoelectric tube 13. Consequently, the useless work 2 is no longer more tense than is required, so that it is not cut and is ground continuously. At the same time, it is possible to prevent the chain rail 1 from becoming bent.