A single information processing device capable of configuring an information system that maintains matching between information retained by a self device and information retained by a partner device in a way that links up a plurality of information processing devices with each other, has a storage unit including a memory cell retaining a predetermined quantity of information and a comparing unit that compares the information retained by the memory cell at the present with information written afresh to the memory cell, an extraction unit extracting the information written afresh to the memory cell about which the comparing unit judges that the information retained at the present is different from the information written afresh, and a transmitting unit transmitting the extracted information to the partner device linking up with the self device.