To provide a circuit module, a bicycle electric component, and a communication system that are easily matched to a communication system that uses power line communication, a circuit module is configured to be mounted on a bicycle electric component. The circuit module includes a first circuit board, a communication converter configured to convert between information appropriate to power line communication and information appropriate to communication other than the power line communication and mounted on the first circuit board, and a plurality of first terminals formed on the first circuit board. The plurality of first terminals is connected to a second circuit board included in the electric component.