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

When a heating plan is determined (S1), the heating line is linearly heated with a heating coil which is numerically controlled by the position information of the heating line (S2), the amount of deviation of a heating line to be next linearly heated is detected from the displacement of marking provided on the metallic sheet (S4) and the amount of deviation is compared with the allowance (S5). When the amount of deviation is within the allowable range, the linear heating of the next heating line is performed (S2). Meanwhile, the amount of deviation of the heating line exceeds the allowance, after analyzing heating deformation generated on the metallic sheet caused by the performed linear heating (S6), the displacement of the nodal point is extracted from the initial shape of the metallic sheet on which the heating deformation analysis is performed in the deformed state (S8), the amount of deviation of composing point of the heating line from the original set position of the heating line heated later is calculated on the basis of the extracted displacement of the nodal point (S9) and the NC data for numerically controlling the heating coil is corrected on the basis of the position information of the heating line after displacement (S10).