An antenna includes a metal tube, a coaxial cable disposed along a central axis of the metal tube, and a variable-impedance transmission wire structure. A dielectric body and a metal part are arranged along an axial direction of the cable. The antenna makes the resulting structure stable and reliable, achieves miniaturization of a multi-band antenna and provides a sufficiently wide bandwidth for each frequency band. The antenna also realizes easy control of the radiation pattern and is convenient for practical applications.