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The number of wireless LAN users is increasing. Therefore, the number of public wireless LAN services is also increasing. However the transmission area of a wireless LAN is not visible to the user. Therefore, it is difficult to control the administration of a wireless LAN. As a result, administrators need to take adequate management against information leakage, eavesdropping and unauthorized access. Administrators need to change the encryption key frequently. However, if the administrator changes the encryption key frequently, this is a burden for administrator and users. If the administrator uses VLC (visible light communication), it is easy to control connections, because VLC has a clear communication area. This is the difference with radios and IR (infrared rays), we can see the communication area of VLC, thus it is easy to control access. Only users in the light area receive the encryption key. The users out of the light cannot receive the encryption key. In this paper we propose a method that distributes encryption keys in a wireless LAN system using VLC. The innovation of this paper is to change the encryption key of a wireless LAN using VLC with no burden on the user. A prototype system is also evaluated. In this sytem, the VLC is also the lighting system. The brightness of the lighting must be constant. Therefore 2 PPM (pulse position modulation) is used. In the experiment, we use very bright LEDs, which are driven by USB bass power. The communication speed, energy bit per noise (Eb/N) and error rate were measured. The error rate is measured by the changing illumination of the LEDs. We also examine the relationship between the communication distance and angle. The reults show that system was useful for encryption key distribution, and we are able to communicate with a convenient and secure wireless LAN.