To reduce interference even when frequencies are duplicated by setting a different spread code to the frequencies to be used each other in the case that channels transmitting data are adjacent to each other.

In a data mode, a master station retrieves a dead data channel (step 110) and after deciding a using data channel (step 120), decides a type of code (step 130). Then the master station transmits a connection instruction to a slave station and after receiving its response (steps 140, 150), transmits/ receives the data according to the channel and the type of code decided in a command mode.