A sound reproducing device includes a decoder section (1200) configured to decode an audio-signal bit stream input from the outside world, and to generate a decoded PCM signal; a control section (1100) configured to identify reproduction conditions from reproduction-instruction information obtained from the outside world and decoding information obtained from the decoder section (1200), and to provide a reproduction instruction; and an additional-audio addition section (1500) configured to process additional audio data input from the outside world, to add a result with the decoded PCM signal, and to output a result as an output PCM signal. The additional-audio addition section (1500) includes an additional-audio generation section (1510) configured to process the additional audio data so that the additional audio data can be added with the decoded PCM signal, and to output a result as an additional-audio PCM signal, and an adder (1520) configured to mix the additional-audio PCM signal and the decoded PCM signal. The additional-audio generation section (1510) includes a plurality of processing means (1511 and 1512) depending on a trade-off between the amount of load of computation process in the processing and acoustic properties of a processing result. The control section (1100) identifies one of the plurality of processing means (1511 and 1512) based on the reproduction-instruction information and the decoding information. The additional-audio generation section (1510) processes the additional audio data by the processing means identified by the control section (1100).