To keep sound communication by stopping the function of a reception side LAN communication controller when message packet interruptions being a fixed number or more occur within a fixed time in the reception side LAN communication controller in packet transmission from a transmission side LAN communication controller.

A distribution system is constituted of computers A-E101, 111 to 114. An abnormality detecting program 116 arranged in the LAN communication controller 106 counts the number of the message packets stored in a reception buffer 117 and monitors the number of the message packet interruptions occurring within the fixed time. When the number of the message packet interruptions occurring within the fixed time is abnormally larger than an index value which is set in accordance with the performance of the computers constituting OS 105, the self processing function of the LAN communication controller 106 is stopped. A configuration control program 104 changes-over a system into the LANB one 110 in order to fetch data from the LAN communication controller 107.