To provide a method for making the number of antennas in a wireless communication system to be minimum.

The repeater of a single antenna is constituted of a single antenna 20 and a related circuit connected to the single antenna. The related circuit has an amplifier 32, and a circulator 22 having a first terminal, a second terminal and a third terminal which are adjacent to one another in the circulating direction. A signal received by the first terminal is sent to the second terminal, a signal received by the second terminal is sent to the third terminal and a signal received by the third terminal is sent to the first terminal. The first terminal is connected to the single antenna, the second terminal is connected to the input of the amplifier and the third terminal is connected to the output of the amplifier.