A coil antenna structure includes a first magnetic component extending in the thickness direction of a tabular primary casing. A second magnetic component and a third magnetic component, which are magnetically connected to the first magnetic component, are disposed on the first principal surface side and the second principal surface side of the primary casing, respectively. The first magnetic component is provided with a coil component surrounding it. In this manner, a U-shaped magnetic path is provided at an end portion of the primary casing so as to detour around a substrate defining an internal conductor. Likewise, a U-shaped magnetic path including fourth to sixth magnetic components is provided in a secondary casing defining a clamshell type casing together with the primary casing so as to detour around a substrate defining as an internal conductor.