PURPOSE: To attain communication even when a switch is failed by providing by-pass lines corresponding to the number of I/O side switches constituting a multi-stage connecting network.

CONSTITUTION: In the multi-stage connecting network for controlling respective PEs 1 from a host 2 through a PE control bus 3 and executing parallel data processing, a prescribed number of by-pass lines 4 are allowed to intersect with communication lines among input and output terminals and I/O switches 6. A by-pass switch 5 is connected to each intersecting point so as not to be overlapped to the intersecting point of another by-pass line. Even when any one of I/O switches is failed in such constitution, the communication line allowing a signal from the input terminal to pass the failed switch is disconnected and a by-pass communication line arriving at the output terminal is connected to another communication line through a by-pass line 4 and by operating the by-pass switch 5 to constitute an available communication line and secure communication. Switching between the by-pass switch 5 and the I/O switch is executed by a change-over switch device 7 through each switching line 8.