In a parking lot management system, which is applied to a parking lot having a plurality of parking spaces, information about parking is wirelessly communicated between a plurality of wireless LAN base stations connected to an interface part and then connected to the Internet, and a plurality of parking condition detection devices or a wireless LAN mobile station installed in a mobile object. The information is managed by a server via an IP network so that the parking lot management system can provide the information for a user who is in the parking lot.