To attain manpower saving and efficiency in the machining of an original plate of a metallic material by retaining the 'habit' data of the metallic original plate as electronic information and providing the collating information for the original plate.

A computer 2 performs process control and data fetch control. A scanning thermometer 6 measures the surface temperature of a steel plate IR after it passes a hot leveler 11, obtaining T(x, y) and determining a residual stress σc, (x, y) by an arithmetic and control unit 4. The host computer 1 takes in the determined value, writes in electronic information or collating information in a storage medium, and also writes in the collating information on the steel plate side.