This paper describes a method for detection of change of enviornmental conditions using analysis of series of wireless LAN signals. The method uses the charcteristics that the signal strength of the wireless LAN changes according to the conditions of the indoor environment such as the number of persons surroundings of the wireless LAN access points and clients. The paper discusses the method for validating the change of the conditions using the measurement of the indoor environment using the imaging devices and the change detection result of the series of the signal strength of wireless LAN system using singular spectrum transformation. We show the feasibility of the proposed method through the system integration and experimental results.