A coil apparatus comprising: a base having a front surface and a rear surface ; a magnetic portion having a front surface and a rear surface, the rear surface of the magnetic portion being provided on the front surface side of the base ; and a coil portion provided on the front surface side of the magnetic portion , the coil portion including a conductive wire , wherein: the base is made of a non-magnetic and electrically conductive material, and the coil portion is a coil in which the conductive wire is wound in a planar spiral shape, having a coil body , an inner lead wire and an outer lead wire , wherein the inner lead wire is an end portion of the conductive wire drawn out from an innermost peripheral end of the coil body , and the outer lead wire is an end portion of the conductive wire drawn out from an outermost peripheral end of the coil body , and both the inner lead wire and the outer lead wire are drawn out to the rear surface side of the base through a common first passing region included in the magnetic portion and a common through-hole included in the base , characterized in that the common first passing region is provided at a center portion of the magnetic portion , and the common through-hole is provided at a center portion of the base . a base having a front surface and a rear surface ; a magnetic portion having a front surface and a rear surface, the rear surface of the magnetic portion being provided on the front surface side of the base ; and a coil portion provided on the front surface side of the magnetic portion , the coil portion including a conductive wire , wherein: the base is made of a non-magnetic and electrically conductive material, and the coil portion is a coil in which the conductive wire is wound in a planar spiral shape, having a coil body , an inner lead wire and an outer lead wire , wherein the inner lead wire is an end portion of the conductive wire drawn out from an innermost peripheral end of the coil body , and the outer lead wire is an end portion of the conductive wire drawn out from an outermost peripheral end of the coil body , and both the inner lead wire and the outer lead wire are drawn out to the rear surface side of the base through a common first passing region included in the magnetic portion and a common through-hole included in the base , the base is made of a non-magnetic and electrically conductive material, and the coil portion is a coil in which the conductive wire is wound in a planar spiral shape, having a coil body , an inner lead wire and an outer lead wire , wherein the inner lead wire is an end portion of the conductive wire drawn out from an innermost peripheral end of the coil body , and the outer lead wire is an end portion of the conductive wire drawn out from an outermost peripheral end of the coil body , and both the inner lead wire and the outer lead wire are drawn out to the rear surface side of the base through a common first passing region included in the magnetic portion and a common through-hole included in the base , characterized in that the common first passing region is provided at a center portion of the magnetic portion , and the common through-hole is provided at a center portion of the base . the common first passing region is provided at a center portion of the magnetic portion , and the common through-hole is provided at a center portion of the base . <EOS>