A communication device selects an optimal modulation method even when a propagation path condition is changed. In the communication device, a second communication device has a transmission path condition estimation unit for estimating the propagation path condition change speed and a communication quality estimation unit for modifying the communication quality estimation method according to the speed of the change of the propagation path condition and for estimating the communication quality according to the modified estimation method. The information on the estimated propagation path condition and the information on the communication quality are transmitted from a transmission processing unit, and an adaptive modulation control unit of the first communication device sets a condition for selecting the modulation method and decides the modulation method according to the set condition and the information on the communication quality.