PURPOSE: To enhance efficiency of line operation, simultaneously grasp conditions of defects occurred, facilitate claim treatment of products and trace defect information on the line by providing a defect sensor in the papermaking line and simultaneously introducing a computer.

CONSTITUTION: A defect sensor 3 for sensing defects of machine-glazed paper and sheet paper produced in a continuous process of a papermaking line is provided and a computer 1 for controlling the aforementioned whole line is simultaneously installed to trace defect information on the above-mentioned machine-glazed paper and sheet paper. The operation of the line is controlled based on the aforementioned defect information. Thereby, defect information on the papermaking line is traced.