To reduce a communication load among data storage devices and data processing devices, a communication device comprises node information storage means for storing identifiers of data devices and processing devices and communication costs, and search processing means for receiving a message, which includes a transfer route of message and a total cost, which is a communication cost of transfer route, and detecting and outputting a closed path, from transfer route, having a negative total cost, or transmitting to the registered data device a message including a new total cost calculated by subtracting a communication cost corresponding to data device concerned from total cost and a new transfer route made by adding communication device to transfer route, and transmitting to the registered processing device a message including a new total cost calculated by adding a communication cost corresponding to processing device concerned to total cost, and new transfer route.