PURPOSE: To maintain the stable message communication even at the time of the change of the condition or a fault or the like with respect to the system for message communication processing among plural processors constituting a parallel computer system.

CONSTITUTION: Time information indicating the transmission time of a message is newly added as discrimination information of this message. Based on contents of the reception message and its time information, a reception destination processor P discriminates whether the message is a new message or a retransmitted message, and the processing corresponding to the discrimination result is performed. A repeating installation N abandons messages received over a certain time after transmission and changes an initially set transmission route to set a bypass route again in the case of a fault in another repeating installation N of the repeating destination. Thus, the load to the communication line is prevented from being quickly increased by the message retransmission processing or the like, and stable message communication is maintained to improve the reliability of the computer system.