A data conversion system for converting data outputted from an information processor into data in a different format in real time while preventing any defect of an image such as frame missing or frame repetition of moving image data by synchronizing data transfer with converted data output. One of first and second nodes on an IEEE1394 bus functions as a cycle master, and first data is transferred from the first node to the second node in synchronism with a cycle start packet outputted from the cycle master. Second data generated by converting the first data by the second node is outputted in synchronism with a reference signal inputted from outside. The system comprises an external synchronizing signal receiving section provided at least in one of the first and second nodes and adapted to receive the reference signal inputted from outside and a synchronism control section for synchronizing the frequency of a cycle start packet outputted from the cycle master with the reference signal received by the external synchronizing signal receiving section.