To provide sampling conversion technology evading sharp increase in the circuit scale of a DV decoder by synthesizing an audio signal with a video signal without newly adding a DA conversion circuit and an AD conversion circuit.

In a system provided with a sampling conversion means for receiving a first audio signal sampled by first sampling frequency asynchronous with a video signal, converting the first audio signal into a second audio signal of second sampling frequency synchronous with the video signal and outputting the second audio signal, the first audio signal is over-sampled by frequency corresponding to the common multiple of respective sampling frequency values of the first and second audio signals which are asynchronous in a short period but synchronous in a long period at the time of converting the sampling frequency.