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.