An information processing system according to the present invention includes: a plurality of processing units; a plurality of input/output units controlled by any one of the processing units; a plurality of first connection units connecting one of the processing units to a first communication channel; a second connection unit connecting the input/output units to a second communication channel; a first mediating unit mediating the second communication channel and a communication network, and transmits identifiers of the input/output units via the communication network; and a plurality of second mediating units mediating a connection between the communication network and the first communication channel, receiving the identifier, and, when an identifier of its own is included in the received identifiers, establishing a connection between the input/output unit with the own identifier and the processing unit and detaches connections between the input/output unit with different identifier and the processing unit.