PURPOSE: To detect simultaneously a defect in the axial direction and a defect in the circumferential direction of a material to be inspected, and to improve the work efficiency by placing a thin film surface so as to be orthogonal to the material to be inspected, displacing relatively a magnetic sensor and the material to be inspected, and detecting a variation of the middle point potential of the magnetic sensor in that case.

CONSTITUTION: A magnetic sensor 5 has a magnetism sensible part which is connected by placing two magnetic resistors A and B obtained by forming a ferromagnetic metallic thin film like a polygonal line, so that the longitudinal directions are orthogonal to each other. Both ends of these magnetic resistors A, B and its middle point are led out and connected to electrodes 51, 52 and 53, respectively. As for the magnetic sensor 5, its resistance is varied anisotropically by an angle made by a magnetizing direction of the magnetic resistor and a direction of a current flowing to said resistor. The magnetic sensor 5 is provided in the vicinity of a steel rod 1 so that the magnetism sensible part is made to coincide with the direction of a magnetic field formed by, for instance, a through-coil 2, and becomes orthogonal to a magnetic field in the Y direction, which is provided by a coil 4 and orthogonal to the direction of the magnetic field. As a result, a bias magnetic field whose direction coincides with a DC magnetic field provided to the steel rod 1 is provided to the magnetic sensor 5, and also a magnetic field orthogonal to the magnetism sensible part (orthogonal magnetic field) is provided.