Provided is a repeater for relaying communication by achieving synchronization with a base station and a mobile station without using GPS. The repeater includes a donor unit communicating with the base station and a remote unit communicating with the mobile station. Upon receipt of a signal from the base station, the donor unit specifies a preamble of the received signal to achieve synchronization with the base station. This determines start of each frame in the communication between the base station and the repeater. After the synchronization achievement, the remote unit starts performing procedures for achieving synchronization with the mobile station. Upon notification of the start timing of each frame from the donor unit, the remote unit determines the notified timing as start timing of each frame in the communication between the repeater and the mobile station, and transmits a preamble referred to by the mobile station when it achieves synchronization.