A terminal apparatus firstly transfers packets of a trial class. When the communication quality is insufficient, the terminal apparatus determines after a predetermined period of time whether or not to transfer the trail-class packets again according to a traffic rate of priority-class packets. There are provided a trial-class band capacity not to discard packets of the trial class and a priority-class band capacity not to discard packets of the priority class. Trial-class packets exceeding the former are discarded but the packets that has once become a priority class will not be discarded unless the latter is exceeded.