A digital data reproducing apparatus and method are provided, which are capable of reproducing both digital audio data from the main body of the apparatus and digital data from an external interface, using a simple construction. A main body of the apparatus processes first digital data, an interface receives, from an external device independent of the main body, second digital data having a sampling rate asynchronous with and different from a sampling rate of the first digital data, the first and second digital data being reproduced by the main body. The first digital data are oversampled at a frequency n times the sampling rate of the first digital data. The first digital data oversampled by the filter device and the second digital data input via the interface are added together, and the resulting data are converted into an analog signal.