an IP layer for storing an IP management table of a corresponding table of a virtual IP address that is an IP address of the virtual computer node and a real IP address that is an IP address of the physical computer node, and performing communication using the virtual IP address based on the IP management table;

a network device connected to other computer node and the client through a network;

an application executing unit for executing an application designated from the client;

a load state detector for detecting a load state of other computer node;

a node assigning unit for assigning the real IP address to the virtual IP address based on the load state to form the IP management table; and

a broadcasting unit for broadcasting the IP management table to other computer node, wherein

the IP layer includes:

a virtual node providing unit for providing the virtual IP address to the client; and

a packet allocating unit for retrieving the real IP address from the virtual IP address by using the IP management table when the packet with the virtual IP address as a destination is inputted from the network device, and outputting the packet with the retrieved real IP address as a destination to the network device,

wherein the packet allocating unit further encapsulates the second IP header with the retrieved real IP address as a destination to the first packet when the first packet added with the first IP header with the virtual IP address as a destination is inputted from the network device, and outputs the obtained second packet to the network device.