PURPOSE: To control the switching position of a polarizer to at least a single polarized wave so as to automatically set the switching position of the polarizer to the surfaces of another polarized waves.

CONSTITUTION: A rotary antenna having a rotational axis parallel to the erath axis is provided with a polarized wave surface switching circuit 1 which outputs a switching signal to linearly change the switching position of a polarizer 2 set in a feed horn by means of the control signal supplied from a control part 9, a storage part 4 which previously stores the data on the satellite names and the incident angles of both horizontal and vertical polarized waves, and a coefficient storage part 5 which stores a coefficient to correct the data stored in the circuit 1. In such a constitution of the antenna, the switching position of the polarizer 2 is changed at least to a single polarized wave signal at the polarized wave surface by the operation of the part 9. Then a coefficient is obtained from the changed variable of the switching position of the polarizer 2 and stored in the part 5. The part 9 reads out the data and the coefficient in response to the input selection signal. Then the part 9 outputs a control signal and supplies it to the circuit 1 to switch the polarizer 2.