To remarkably reduce burden loaded to master radio equipment and to surely and efficiently perform the initial synchronization in a radio system for automatic meter reading.

When the initial synchronization is requested from a slave radio equipment, the transmission of initial synchronization request signals for fixed time and the reception for judging the presence/absence of a response signal from the master radio equipment are repeatedly performed at specified timing. This operation is executed until the response signal from the master radio equipment is received. Relating to the master radio equipment, wait reception including carrier sense is performed in a fixed cycle and when the initial synchronization request signal from the slave radio equipment is received, the response signal containing its own clock information is transmitted at the specified timing. Relating to the slave radio equipment, when the response signal from the master radio equipment is received, its own clock is matched and synchronized with the clock of the master radio equipment corresponding to the clock information of the master radio equipment contained in this response signal.