Generally speaking, APs of existing IEEE 802.11 wireless LAN system may be always turned on in many cases even though no STA is present. Such APs may consume unnecessary electricity and that means electricity consumption. In this paper, we propose "Green Wireless LAN System", which reduces electricity consumption by automatically turning on or off APs in accordance with presences of STAs. In the system, we propose how to detect presences of STAs, how to authenticate and authorize STAs and how to turn on or off an AP in order to maximize electricity conservation. Also, we implement the proposed system. Then, we experiment on it in order to clarify how long it takes that an STA associate with an AP and what cause its delay. In addition, we measure how much electricity APs consumes in the system. Finally, we simulate how much electricity consumption the proposed system can reduce based upon results of experiments and actual usages of the existing wireless LAN System.