A shared antenna communicates radio waves with different frequencies or different polarization characteristics, and has a simple configuration that can be placed in a small device. The antenna includes a plurality of loops of the shape of a cross in a spiral fashion and includes a gap provided at a certain midpoint in the spiral loops and a power supply portion provided in a central portion. The distance of the gap is set such that electromagnetic coupling is caused at a first frequency and no electromagnetic coupling is caused at a second frequency different from the first frequency.