A radio wave receiver comprising an antenna structure placed within a case. The antenna structure has a rod-like core around which a coil is wound. A pair of opposite external magnetic members are each provided in a respective one of a pair of cavities provided so as to extend along the inner periphery of the case from adjacent the respective ends of the rod-like core toward the end points of an inner diameter of the case parallel to the axis of the rod-like core. The pair of external magnetic members is substantially the same permeability as the core. Thus, the antenna core is magnetically coupled to the pair of external magnetic members.