To provide an antenna unit whose antenna characteristic can be adjusted conveniently in a process close to shipping of portable radio equipment, an antenna system using the antenna unit and the portable radio equipment.

The antenna unit 15 is constituted of an insulating base 18 supporting radiation conductors 16a and 16b constituting first and second antenna elements. An antenna element to be used is switched by the direction of mounting at the time of mounting the antenna unit 15 on a mounting object such as a circuit board, Both antenna elements have respectively different first and second feeding points 17a and 17b, and both feeding points are arranged at positions where different faces of the insulating base 18 correspond. After deciding the antenna element to be used, a mounting inhibiting means for inhibiting one mounting face of both antenna elements from being mounted on the mounting object may be provided.