PURPOSE: The titled detector which can directly, accurately detect the expansion, by detecting the expansion of the roll diameter depending on the axial expansion of the roll.

CONSTITUTION: The work roll 15 is driven by the driving motor 14, and the temperature of the work roll 15 rises up; then, if the backup roll 11 expands due to its temperature, the load of the load cell 10 on both sides increases through the spring 12, and its load signals F1, F2, are amplified 17 through the filter 16, and are summed 18 into the load signal F. This load signal F is added 20 to the memory value F0 being stored in the memory circuit 19 when the draft position of the roll is calibrated; as a result, the increment ΔF is obtained. This increment ΔF is proportional to the axial expansion ΔL of the backup roll 11. Accordingly, from this result, the expansion ΔD of the diameter of the backup roll 11 is obtained (arithmetic circuit 22), and its signal is inputted into the sheet gauge controller.