A data processing unit to that reliably avoids a deadlock condition regardless of status of a ring bus occupied with normal data packets. The data processing unit comprises ring bus, a plurality of data processing units connected to the ring bus, for mutually performing data exchange using a packet circulated on the ring bus and a injection unit for injecting a special packet distinguished from the packet on the ring bus so as to circulate the special packet on the ring bus, wherein the plurality of data processing units respectively comprise for confirming whether or not a transmission destination data processing unit of the data is capable of receiving data by using the special packet, and a transmission unit for transmitting the data to the transmission destination data processing unit using the special packet.