To prevent the load on a monitor computer from increasing even when computers connected to a network increase in number by decentralizing a transmitting process for a health check control message to plural computers and using only one check machine, and sending only a notice message to a monitor master.

The transmitting process for the health check control message is decentralized to plural computers connected to a network and only one check machine is defined; and only the notice message such as a fault notice is sent to the monitor master. For example, computers 100-1 to 100-5 are connected to the network 101 and the computer 100-1 is used as the monitor master A. To a computer having sent a notice of actuation, the instruction is male that a health check, on a computer having sent a notice of actuation right before it, is started. Then the monitor master A itself makes a health check on the computer having sent a notice of actuation most recently.