PURPOSE: To detect a flaw of the roll barrel part during operation by arranging ≥1 probe for eddy current flaw detection in a milling machine closely to the surface of the roll barrel part and displaying abnormality signals from those probes.

CONSTITUTION: The probes 1 are fitted to a protection plate 7 and a hollow pipe 10 where small holes for passing a cable to the probes 1 are provided in one direction and a rubber wheel part 3 which is driven by the roll barrel end part in contact are fitted to the protection plate 7. Further, a support rod 9 is fitted to the pipe 10 and supported on a support arm 4 fitted to a milling machine stand. The probe 1 for eddy current flaw detection detect differences between exciting magnetic flux at a normal position on a surface to be inspected and exciting magnetic flux which becomes different owing to structure variation due to cracking or thermal influence. Their electric signals are passed through the cable and amplifiers to sent and display whether or not there is abnormality on a display part.