To compose both an active system and a standby system with general servers for which no special function is required, in order to achieve cost reduction.

While a telephone switching system 1 as a communication system with a redundancy composition is selectively connected with a counter network 40 including communication terminals through a first network 30, it is provided with a first and a second servers 10, 20 which are mutually connected through a second network 50, and the first and the second servers 10, 20 are provided with: call distribution function units 11, 21 which have a function to distribute calls sent from respective counter network 40 to a server of an either side; and call processing function units 12, 22 which have a function to process the distributed calls from respective call distribution function units 11, 21.