A coil apparatus for use in a transcranial magnetic stimulation apparatus is provided in which the coil apparatus includes a coil arranged to oppose a surface of a head of a human to generate a current by an induced electric field in a magnetic stimulation-target region in a brain by electromagnetic induction, and to stimulate neurons. The coil apparatus includes the coil configured by winding a conductive wire along a predetermined reference surface； and a magnetic body arranged between the head and the coil to oppose the coil, and arranged at a position at an opposite side of the head. The magnetic body is provided for flowing a current therein by an induced electric field when the coil is driven, and for increasing the current flowing by the induced electric field in a magnetic stimulation-target region of the brain as compared with that with no magnetic body.
