A computer cluster arranged at a lattice point in a lattice-like interconnection network contains four nodes and an internal communication network. Two nodes can transmit packets to adjacent computer clusters located along the X direction, and the two other nodes can transmit packets to adjacent computer clusters located along the Y direction. Each node directly transmits a packet to an adjacent computer cluster in the direction in which the node can transmit packets, when the destination of the packet is located in the direction. When the destination of a packet to be transmitted from a node is not located in the direction in which the receiving node can transmit packets, the node transfers the packet to one of the other nodes through the internal communication network for transmitting the packet to the destination of the packet through the one of the other nodes.