A telephone switching system includes line packages and a switch unit allowing a path to be established between the line packages. At least one line package is interconnected to, e.g. a broadband-adaptive unit, and is adaptive to both of a first coding rule expected of the switch unit and a second coding rule higher in compression ratio than the first coding rule. The broadband-adaptive line package, monitoring the coding rule of another line package connected thereto, adapts itself to the first coding rule if the other line package is adaptive only to the first coding rule, or adapts itself to the second coding rule if the other line package is adaptive to both of the first and second coding rules.