To unnecessitate the preparation of a front end processor dedicated for backup by distributedly connecting a line connected to the front end processor causing a fault to the idle channels of the other plural normal front end processors.

A line switch control part 22 controls the connection setting of a line at the line setting part of a line switcher. This line setting part is controlled through a communication medium. When the fault occurs in any front end processor 20 and its performance is disabled, the connection setting of the line at the line setting part of the line switcher is changed under the control of the line switch control part 22 at any other normal front end processor 20, and the line connected to the front end processor 20, where the fault is generated, is distributed to the other normal front end processor 20. Thus, the front end processor 20 where the fault is caused is backed up and service for terminal equipment is maintained.