In a mobile station apparatus and a base station apparatus in a digital mobile communication using a TDD system and a CDMA system, in the case where there is a difference in communication qualities between a revere link and a forward Link, a burst length of a communication link with lower quality can be made longer than a burst length of a communication link with higher quality. That makes it possible to communicate more signals in the communication link with low communication quality than in the communication link with high communication quality, which allows the equal communication qualities in the reverse link and the forward link.