A bus arbitration system employs counters respectively provided for an encoding section and an decoding section that are started when there is a request signal from the respective encoding section and decoding section. The counter values are outputted to respective comparators that compare the counter values with predetermined values and the results of the comparisons are fed to an arbitration controller. The arbitration controller in turn determines priority rankings for the encoding section and the decoding section based on the signals inputted from the comparators and outputs an acknowledgement signal to the module that has the highest priority.