PURPOSE: To perform a load distribution switching to a call processor dynamically by redistributing signals unreceivable on the call processor to other call processors according to a former state corresponding load distribution table.

CONSTITUTION: Signals inputted to a signal processor 1 are distributed at a signal distributing control part 2 through routes S1-S3 to call processors 3-5 based on a new state corresponding load distribution table 6. The respective processors 3-5 perform call processing when the received signals are receivable signals in the call state at this time, and redistribute them through the routes of S4-S9 to other call processors according to the former state corresponding load distribution tables 10-12 when they are unreceivable signals. Thus, it is not necessary to turn corresponding lines to an unusable state at the time of extension/reduction of level 4 call processors, line number assignment can be freed. Also, since the lines do not turn to the unusable state at the time of the failure of the level 4 call processor. Thus, the processor is not loaded further at the time of overloading.