To eliminate the generation of a scratch in a bar-shaped specimen by arranging at least two roller devices at a position before or after a probe in a guide sleeve into which the specimen is inserted to fix a passing core position of the specimen.

Inlet and outlet side guide sleeves 3a and 3b are arranged in contact with an eddy flaw detector 1 to guide an specimen 2 as atomic fuel bar cover tube, for instance, and a probe 4 for scratches is provided therebetween. For example, more than one roller devices 7 which each comprise upper and lower rollers 7a and 7b pivoted on a roller holder having a spring for urging and an adjusting piece for fine positional adjustment are arranged on the guide sleeves 3a and 3b at a position before and after the probe 4 so as to always keep constant the axial position of the object 2 to be inspected along the length thereof. This eliminates slide contact with the internal surfaces of the guide sleeves 3a and 3b and also hold a clearance with the probe 4 constant when the object 2 to be inspected is inserted for eddy detection of flaws.