Abstract: A line switching apparatus is adapted for use with a communication apparatus which comprises a plurality of lines which are accommodated according to a key number system, a plurality of ports which aer connected to communication terminals, and a matrix switch which couples the lines and the ports. The line switching apparatus comprises an auxiliary apparatus, and a control part for detecting an arbitrary one of the ports which is down and not capable of making a communication, disconnecting the arbitrary port from one of the lines and connecting the one line which is originally connected to the arbitrary port to a port which is originally connected to a line of a last key number, and connecting the line of the last key number to the auxiliary apparatus.