To provide a cities digital multi-address line system which automatically sends a relay wave or broadcasting wave, when a proxy master office is operated, and receives stably on the slave office side.

When a receiving state monitoring function is added to a portable wireless installation and the portable wireless installation is activated by a user's operation, first, all the receiving states of the relay waves and broadcasting waves are monitored. The portable wireless installation changes the setting automatically, in response to the receiving state of the relay wave and broadcasting wave and sends either the relay waves or the broadcasting waves at broadcasting activation.