Thickness controlling method and rigidity monitoring method for rolling mill

A thickness controlling method for a rolling mill that rolls a material to be rolled so as to have a target thickness, the thickness controlling method comprising:

• a step of using a regression model to recursively approximate a relationship between a roll force change amount between a preceding material and a present material and a gap error change amount of the rolling mill, and predicting a gap error in a rolling of the present material on the basis of the regression model, the preceding material being a rolled coil rolled by the rolling mill immediately prior, and the present material being another rolled coil to be rolled following the preceding material;
• a step of correcting a gap setting amount in the rolling of the present material, on a basis of a value of the predicted gap error;
• and
• a step of updating a regression coefficient of the regression model, on a basis of an actual roll force and an actual gap error change amount obtained from the rolling of the present material.