A data processing apparatus can reduce an occupancy rate of a ring bus by suppressing occurrence of a stall packet, and can change a processing sequence. In the data processing apparatus, a buffer is provided in each communication unit connecting the ring bus and the associated processing unit. Transfer of data from the communication unit to the processing unit is controlled by an enable signal. Consequently, occurrence of a stall packet is suppressed. Accordingly, frequency of occurrence of a deadlock state is reduced by decreasing the occupancy rate of the ring bus.