signal level of desired channel n is smaller than neighboring channel n 1 or n 1 by 5 db in the output of vif circuit 9 the signal level of desired channel n is larger than the neighboring channels by 15 db as shown in fig9 d further when the polarizer 2 is set for a vertically polarized wave in the output of vif circuit 9 the signal level of desired channel n is larger than that of the neighboring channels by 30 db anyway because the signal level of desired channel n is larger than that of the neighboring channels by at least 15 db irrespective of the polarization plane of polarizer 2 the relation between the polarization plane of polarizer 2 and the output of detection circuit 16 becomes as shown by the solid line in fig4 a therefore the desired polarization plane can be easily determined in this embodiment memories 36 and 37 for storing data of the sweep voltage are provided to quickly determine the desired polarization plane of polarizer 2 the memory 36 is provided for a vertically polarized wave and the memory 37 is provided for a horizontally polarized wave when ac power supply switching circuit 34 is closed or an antenna switching circuit 30 is operated for changing an angle of the antenna a polarization plane control circuit.