PURPOSE:To perform judgement of internal defects and material of conductive materials and measurement of their thicknesses or the like providing an intermediate magnetic pole between an ultrasonic wave exciting coil and a detecting coil. CONSTITUTION:When a high frequency pulse current is flowed to an ultrasonic wave exciting coil 29 from a high frequency pulse current source 9, eddy current 30 distributing in circular form parallel to the surface is generated by electromagnetic induction in a conductive material 3. The eddy current 30 and magnetic fields 27 produce vibrating force 31. This vibrating force 31 advances in the direction of an arrow 32. When it arrives at an internal defect, it is reflected thereby and advances in the direction of an arrow 33. And vibrating force 34 is produced. This produces eddy current 35. This eddy current 35 is detected by a detecting coil 36. Here, provision of an intermediate magnetic pole 24 between the ultrasonic wave exciting coil 29 and detecting coil 36 enables electromagnetic coupling of both coils to be perfectly cut off and enables dead zone by transmission pulses to be considerably reduced.