Communication system for making carrier synchronous

In a communication system having a base station (1) and terminal stations (5-1 to 5-M) in two-way communication, frequency converters (12-1 to 12-N) transmit transmitting signals. The terminal stations transmit channel selection signals to the base station. A level controller 15 discriminates, in response to the channel selection signals from the terminal stations, each of the channels that is selected by the terminal stations and produces and supplies a level control signal to the respective frequency converters. The selected frequency converter increases a level of the transmitting signal that corresponds to the channel which is selected by a terminal station.