PROBLEM TO BE SOLVED: To provide an inspecting device for exactly inspecting a differential transformer, even when the fluctuating amounts of the differential output of a differential transformer at the time of impressing an alternating magnetic field for inspection is largely varied for each product. SOLUTION: In a state in which an output voltage at the time of the power supply of a differential transformer 1 is held by a hold circuit 22, the power source of an alternating magnetic field generating circuit 20 for inspection is supplied, so that an alternating magnetic field for inspection can be impressed to the differential transformer 1. When the output voltage of the differential transformer 1 fluctuates to a positive side, the output voltage of the hold circuit 22 is compared with the output voltage of a positive side reference voltage circuit 24 by a positive comparator circuit 26. When the output voltage of the differential transformer 1 fluctuates to a negative side, the output voltage of the hold circuit 22 is compared with the output voltage of a negative side reference voltage circuit 25 by a negative side comparator circuit 27, and quality is discriminated. Thus, the difference of the differential outputs before and after the alternating magnetic field for inspection is impressed can be detected, regardless of the polarities of the differential outputs so that the quality discrimination of the differential transformer 1 can be conducted exactly, even if the differential outputs are unstable. Also, the alternating magnetic field for inspection is impressed after the power supply of the differential transformer 1, so that the changing amounts of the differential output of the differential transformer 1 can be increased, and the quality discrimination can be conducted exactly.
