A detecting device is mounted in a parking lot including parking regions, and can communicate with a cloud server and one mobile terminal entering the parking lot. The cloud server stores an electronic map of the parking lot. The detecting device includes a distance sensor and a positioning device. The distance sensor detects occupied information of each parking space of each parking region and transmits the occupied information to the cloud server. The positioning device detects an original location of one mobile terminal entering the parking lot and transmits the original location to the cloud server, so that the cloud server can update the electronic map to indicate the occupied information and the original location.