To provide a method of straightening defect in the shape of a metallic sheet and reducing residual stress with a roller leveler.

When straightening the metallic sheet with the roller leveler by setting the amounts of pressing on the inlet and the outlet sides so that the flatness of a steel sheet after straightening is a target value while taking straightening load as a target value to impart a prescribed plastic deformation rate to the steel sheet, in the case where a straightening load and/or the actual value of the flatness of the steel sheet which are obtained by a first straightening are different from the target values, correction for equally increasing and decreasing the amounts of the pressing on the inlet side and the outlet side is performed at the next straightening and the straightening at the new amount of the pressing by the correction is repeated until the actual values of the straightening load and the flatness of the steel sheet become the target values.