PURPOSE: To make easy to confirm flaws at the repair of crack-found parts, by performing automatic crack finding lengthwise a long material and performing again automatic marking toward the end of long material at the marked part.

CONSTITUTION: Among marking elements 4,... of multichannel located from the circumferential direction to the center, based on the flaw position signal from a crack finder from a multichannel marking device 3, the marking element at the said location is operated, and after performing the mark 5 to the flaw 2 of a steel rod 1, the marking element with marked position is again operated at the final end of the steel rod for marking 6. Further, if a plurality of flaws are present on the circumference of a rod steel, the marks 6 of the number corresponding to the number of marking elements 4 provided with the mark 5 to the respective flaws are made to the steel rod end.