The present invention addresses the problem of checking defects of a rail for a vehicle with a high SN ratio. A detection device (2) for generating check data related to the defects of a railway rail RR (rail for a vehicle) is provided with an oscillating coil C1 (211) and an oscillating coil C2 (211) that are disposed on the surface opposite the railway rail RR and generate AC magnetic fields whose directions are opposite to each other, and a receiving coil (212) that is positioned between or in the vicinity the oscillation coils and that outputs a magnetic field waveform based on the magnetic fields received from the oscillating coils as the check data.
