A data communication apparatus has a data retainer, a retain state manager, a guaranteed bandwidth manager, a surplus bandwidth manager managing outputting of output data having a destination retained in the data retainer to an output line on a per-destination basis when the output data is outputted to the output line with the use of a surplus bandwidth that is a surplus over a sum of guaranteed bandwidths, and a scheduler scheduling outputting of data retained in the data retainer to the output line, based on results of managements by the guaranteed bandwidth manager and the surplus bandwidth manager and a retain state managed by the retain state manager. The apparatus manages the bandwidth with improved accuracy at the time of communication using a surplus bandwidth.