To provide a small-sized integrated antenna system that is used for a portable terminal device and a navigation device contained in a common case and has an excellent operating characteristic for both devices.

The antenna system consists of a unipole antenna 5 placed on an upper face 8A of a case 8 and of a microstrip antenna 10 placed on the upper face 8A of the case 8 adjacent to the unipole antenna 5, and has a wide area common ground plate 11 consisting of the upper face 8A and part of a side face adjacent thereto and an extended ground plate section 12. The unipole antenna 5 is fitted retractively to a mount hole 13 at a half of the common ground plate 11, and the microstrip antenna 10 has a radiation element 1 placed on the other half of the common ground plate 11 via a dielectric plate 3. Both antennas are placed on the upper face 8A of the case 8 for a portable telephone unit 18 and a navigation unit 17 with high sensitivity and directivity, and each unit can properly be operated with the excellent antenna characteristic close to the theoretical characteristic on the wide ground plate.