An information processing system includes information processing devices and relay devices to relay data between the information processing devices, the relay devices each including communication ports, a transmission/reception control unit to cause a first transmission/reception operation and a second transmission/reception operation to be selectively executed, the first transmission/reception operation being an operation in which data is transmitted and received at a first transmission speed, the second transmission/reception operation being an operation in which data is transmitted and received in parallel at a second transmission speed lower than the first transmission speed, and a data division unit to generate pieces of division transmission data whose number is equal to the number of the communication ports by dividing transmission data to cause the generated pieces of division transmission data to be transmitted through the respective communication ports, when the second transmission/reception operation is selected.