Frames in a variable length frame format which are addressed to a plurality of users are multiplexed and preferably transmitted.Data frames having different lengths are multiplexed on a same time through space division multiple access, but since the multiplexed frames are transmitted while eventually having a same length, when the multiplexed data frames from the access point STA0 are received in the respective communication stations STA1 to STA3 in FIG. 4 or when data simultaneously transmitted from the respective communication stations STA1 to STA3 are received in the access point STA0 in FIG. 5, it is possible to eliminate an operation instability of AGC.