As portable information devices with a wireless local area network (LAN) interfaces, such as smartphones and tablet computers, become increasingly widespread, high station density and accompanying severe area throughput degradation are becoming more commonplace. One factor related to this situation is that the initial minimum contention windows size (CWmin) value in current Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) systems is set too low for the number of accessing stations. Because small CWmin values are unsuitable for high station densities, frame collisions become more commonplace and per-station communication performance decreases. In this paper, we assume that numerous stations are connected to a single access point (AP) and propose a media access control method for high station density network. In our proposed method, the AP periodically measures channel utilization and the number of stations that are transmitting frames to the AP, and then modifies the CWmin value based on these parameters. The AP then uses a beacon signal to inform the stations accessing the network of the new CWmin value. To verify the performance of our scheme, QualNet network simulations were performed, the results of which show us that, in terms of throughput, our proposed method outperforms conventional CSMA/CA schemes in wireless LAN environments with high station densities.