To obtain a communication apparatus capable of reducing the consumption of electric power.
A communication system according to the present disclosure includes a transmitter that generates a first signal including communication data and sends the first signal through a communication terminal in a first operation mode, and that generates a second signal including a predetermined first signal pattern and having a transition rate lower than the first signal and sends the second signal through the communication terminal in a second operation mode, and a controller that sets an operation mode for the transmitter to either of a plurality of operation modes including the first operation mode and the second operation mode.