To enable a heating coil to be arranged on a heating line even when a metallic sheet is deformed on the way of actual heating step of linear heating.

When a heating plan is determined (S1), deformation generated on the metallic sheet is analyzed whenever each heating line on the metallic sheet having an initial shape is successively heated (S2), the amount of deviation from the original set position of the heating line which is deviated by the deformation of the metallic sheet is detected (S4) and it is compared with the allowance (S5). When the amount of deviation is within the allowable range, the next heating line is added (S6) and the analysis of the heating deformation of the metallic sheet is again performed. When the amount of deviation exceeds the allowance, the displacement of a nodal point from the initial shape of the metallic sheet on which the analysis of heating deformation is performed in the deformed state is extracted (S8), the amount of deviation of the composing points of the heating line which meets the heating order hereafter from original set position on the basis of the extracted nodal point displacement (S9) and an NC data for numerically controlling the heating coil in the real heating step is corrected on the basis of the position information of the heating line after displacement (S10).