To provide an antenna that is contained in a flat case 12 with excellent anti-vibration and weight-reduction.

A ground plate 14 made of a conductor is placed in a flat package case 12, posts 30 are penetrated through the ground plate 14 at a bottom face of the case 12 and stood upright by integrally forming the posts 30 with the case 12 by an insulating resin. An antenna element 18 is fixed to the tip of the posts 30 by thermally melt-sticking to be placed nearly in parallel on the front side apart from the ground plate 14. A center conductor 28a of a coaxial cable 28 is electrically connected to the antenna element 18 and an outer conductor 28b is electrically connected to the ground plate 14.