The present invention provides a coil device for use in a transcranial magnetic stimulation device, and capable of increasing the strength of the electric field on a head surface. Thus, a coil device for use in a transcranial magnetic stimulation device that positions a wound coil on or near a head surface, and stimulates neurons by producing an electric current from an induced electric field in a magnetic stimulation target region inside the brain as a result of electromagnetic induction, wherein: the wound coil is equipped with a near-head-surface conductive wire section positioned on or near the head surface, and a far-head-surface conductive wire section positioned farther from the head surface than is the near-head-surface conductive wire section； and the distance between the near-head-surface conductive wire section and the far-head-surface conductive wire section is set so as to change in a manner such that the strength of the induced electric field increases in comparison to the region surrounding the magnetic stimulation target region.
