PURPOSE: To provide an antenna and a miniaturized portable radio set capable of detecting the posture of the radio set, automatically selecting an optimum antenna operation mode in accordance with the posture and always obtaining an optimum antenna sensitivity.

CONSTITUTION: A loop is formed by two conductors, the 1st and 2nd loop antennas 11, 12, and one terminal of the antenna 11 is connected to th 1st varicap diode 15 and the other terminal is connected to one terminal of the 2nd varicap diode 14. One terminal of the 2nd loop antenna 12 is connected to the other terminal of the 2nd varicap diode 14 and the other terminal of the 2nd loop antenna 12 is connected to a high frequency grounded surface 18 on a circuit board to constitute a loop antenna.