PURPOSE:To achieve a highly accurate detection by arranging a magnetic flux transmission circuit which has a probe coil applying a printed coil so set to face an object to be measured and a SQUID provided within a range of being reached by a magnetic flux generated from the circuit. CONSTITUTION:A diamond thin film 4 is arranged on the side facing an object 2 to be measured of a pickup coil 3. This eliminates a damage to a pickup coil 3 otherwise caused by a ruggedness of the surface of a sample while enabling the coil 3 to approach the object to be measured as close as several mum. This also can keep a distance to the object to be measured constant. Thus, a higher sensitivity and a higher reliability are achieved as magnetic flux meter, thereby permitting highly accurate detection of a degree of degrading of a ferrite-containing stainless steel which is used under a high temperature environment of a chemical plant, nuclear power plant or the like.
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