A transmitter and receiver apparatus operable to transmit signals from a common antenna during a transmitting period and to receive signals through the common antenna during a receiving period in a time divisional manner, the transmitter and receiver apparatus comprising: a first directional coupler having a first, a second and a third ports for receiving a signal through the first port, and outputting a first signal through the second port and a second signal through the third port, the first and the second signals being of phase difference by 90 degrees each other; a first switch including a first input terminal connected to the second port, a first output terminal, and a second output terminal, for switching between a first connection state during a passage mode in which the first input terminal is connected to the first output terminal and a second connection state during a block mode in which the first input terminal is connected to the second output terminal; a second switch including a second input terminal connected to the third port, a third output terminal, and a fourth output terminal, for switching between a third connection state during the passage mode in which the second input terminal is connected to the third output terminal and a fourth connection state during the block mode in which the second input terminal is connected to the fourth output terminal; a first reception amplifier for amplifying a signal outputted from the first output terminal; a second reception amplifier for amplifying a signal outputted from the third output terminal; a transmission amplifier; and a reception and transmission switching circuit for sending a signal outputted from the transmission amplifier to the common antenna during the transmitting period and sending a signal sent from the common antenna to the first port during the receiving period, wherein one or both of the first switch and the second switch are arranged to switch to the passage mode during the receiving period and to the block mode during the transmitting period. a first directional coupler having a first, a second and a third ports for receiving a signal through the first port, and outputting a first signal through the second port and a second signal through the third port, the first and the second signals being of phase difference by 90 degrees each other; a first switch including a first input terminal connected to the second port, a first output terminal, and a second output terminal, for switching between a first connection state during a passage mode in which the first input terminal is connected to the first output terminal and a second connection state during a block mode in which the first input terminal is connected to the second output terminal; a second switch including a second input terminal connected to the third port, a third output terminal, and a fourth output terminal, for switching between a third connection state during the passage mode in which the second input terminal is connected to the third output terminal and a fourth connection state during the block mode in which the second input terminal is connected to the fourth output terminal; a first reception amplifier for amplifying a signal outputted from the first output terminal; a second reception amplifier for amplifying a signal outputted from the third output terminal; a transmission amplifier; and a reception and transmission switching circuit for sending a signal outputted from the transmission amplifier to the common antenna during the transmitting period and sending a signal sent from the common antenna to the first port during the receiving period,