Premature using an eddy current flaw detector according to the invention, and comprising a preceding roller to perform a preceding processing in the supplied base material processing section, the hardness distribution and a defect of the base material through the eddy current inspection before the base material is supplied to the processing unit and the base material check unit for checking whether or not, the base material by the eddy current signal measured by the inspection analysis and calculating a hardness of the base material, and a control unit for transmitting a control signal to the driving unit to determine the defect to, call processing according to the signal of the controller drive section for driving and characterized in that it comprises a sensor for measuring the pressure applied to the position and the preceding roller of the said rolling roller. Further, eddy current precursor processing method using eddy current in accordance with the present invention, a precursor processing method using an eddy current flaw detector according to the present invention, a base material supply step of supplying a base material to be machined in premature and, before the base material is processed in a preceding roller and the base material eddy-current flaw detection step to check the eddy current of the base to the flaw detector, and hardness calculation and defect determination step that the eddy current analysis of the induced current value measured in the inspection step to calculate the hardness of the base material, and to determine the defect to a base material, the characterized in that it comprises a rolling process step of processing the base material according to the hardness processing mode for determining the machining conditions corresponding to the hardness value calculated in the calculation step the selection step and the processing conditions for the processing mode selected by the processing mode selection step do.