In real time communication, long interruption of a media data signal caused by underflow or overflow of a buffer is reduced. A monitoring unit 35a monitors a state of the buffer 34 periodically. When the number of encoded data in the buffer 34 shows tendency of increasing from a standard data storage number, successively a predetermined number of times, then, it is judged that the buffer tends to overflow. And, the decoding unit 35 is made to skip at least one encoded data to be read and processed this time from the buffer 34. Further, when the number of encoded data in the buffer 34 shows tendency of decreasing from the mentioned standard data storage number, successively the predetermined number of times, then, it is judged that the buffer tends to underflow. And, the processing unit 35 is made to suspend operation during at least one period of the above-mentioned reproduction period.