PURPOSE: To shorten communication time and to increase communication within a fixed time by connecting a transmission line switching means between plural signal transmission terminals and a data processing unit and executing switching corresponding to a switching control signal from the unit by a transmission switching means.

CONSTITUTION: The data transmitter is constituted of a CPU 1 arranged on a node to be a part of a transmission line network(NW) and a transmission line switching router 2 arranged among plural signal transmission terminals T0 to T3 connected to the NW and capable of switching a connection format in accordance with control information. The router 2 turns connection between serial lines S0 to S3 of the CPU 1 and the terminals T0 to T3 to a disconnected state, mutually connects the terminals T0, T1 as one connection format of a routing pattern and mutually connects the terminals T2, T3 to obtain the connection format of the routing pattern. When it is unnecessary to supply a telegraphic message to the CPU 1, the same connection format as the connection of another node through the router 2 of the node concerned is obtained.