To improve the control accuracy of a plate temperature in a continuous treatment line provided with a cooling zone for cooling a plurality of steel plates by a blower and an induction heater for heating the steel plates in the post stage of the cooling zone.

Existence or nonexistence of a change in passing conditions is judged and when the judgment is made that there is the change in the passing conditions, an IH inlet side plate temperature prior to the change of the passing conditions is calculated and an IH inlet side target plate temperature after the change of the passing conditions is calculated, and the calculated IH inlet side target plate temperature is outputted as a command value to the IH 103; and the number-of-revolution command value of the blower is determined and outputted (feed forward control) based on the calculated IH inlet side plate temperature and calculated IH inlet side target plate temperature. On the other hand, when the judgment is made that there is no change in the passing conditions, the IH inlet side plate temperature is calculated and the number-of-revolution command value of the blower is determined and is outputted based on the calculated IH inlet side plate temperature and the IH inlet side target plate temperature calculated at the change of the previous passing conditions (feed backward control).

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