PURPOSE: To keep the satisfactory reception of AM broadcasting day and night and to make an easy automatic channel selection of the required broadcasting station at night.

CONSTITUTION: The system is provided with a reversible motor 3 expanding the antenna element of an on-vehicle radio 1, a positive/reverse changeover switch 4 switching the a motor 3, and a motor control section 5 controlling the expansion amount of the antenna element by performing the rotation amount control of the motor 3 and the switching control of the positive/reverse changeover switch. An optical sensor 6 and the on-vehicle radio 1 are connected to the control section 5. The control section 5 controls the rotation amount and the positive and reverse rotation of the motor 3 so that the expansion amount of the antenna element at night-time AM reception should be shorter than that of the daytime AM reception based on the signal form the on-vehicle radio 1 and the signal from the optical sensor 6.