PURPOSE: To more naturally reproduce analog data so that a time series is not delayed or does not sway as much as possible at an output destination when the analog data to continue time sequentially like a sound or a moving picture, etc., is communicated by converting it into digital data.

CONSTITUTION: A state from a place to send the data up to the place to reproduce the data such as the state of a communication line and the state of an output device, etc., is supervised by the supervisory parts 31 and 32 of the computer (b) of an output side, and this information is known by the computer (a) of a data sending side, and a coding method into the digital data or coding rate most suitable to this state is determined by determining parts 6, 7, 8, and the data is converted and communicated in conformity with these. The data transmitter (a) can acquire the state at each place even during communication, and thus, it communicates the data while changing the method into the most suitable one as occasion calls.