A coil apparatus for use in a transcranial magnetic stimulation apparatus is provided to further increase an electric field intensity on a head surface. The coil apparatus includes a wound-wire coil disposed on or near a head surface so as to generate a current by an induced electric field through electromagnetic induction in a magnetic stimulation-target region of a brain for stimulating neurons. The wound-wire coil includes a near-head-surface conductive wire portion disposed on or near the head surface, and a far-head-surface conductive wire portion disposed farther from the head surface than the near-head-surface conductive wire portion. A distance between the near-head-surface conductive wire portion and the far-head-surface conductive wire portion is set to be changed so that an intensity of the induced electric field becomes larger than that of a surrounding region of the magnetic stimulation-target region.
