An input switching device is provided between a plurality of functional blocks (NoC routers or IP) connected to a specific router among a plurality of NoC routers of a NoC system and the specific router. The specific router includes a plurality of first buffers that temporarily store flits from the input switching device. A plurality of second buffers in the input switching device correspond to the respective one of the plurality of functional blocks, and temporarily store the flits from the functional block. A controller selectively sets one of the plurality of first buffers as output destination of the flit stored in each of the second buffers based on a free space of the plurality of first buffers. A distributor outputs the flit stored in each of the second buffers to output destination set for the flit by the controller. In this way, throughput degradation of the NoC system can be prevented.