To provide an antitheft system for detecting theft, and for outputting warning by detecting the movement of the location of an article, wherein the start/end(warning operation mode/warning release mode) of the operation of an antitheft device corresponding to the state of a user and an article is automatically executed.

The location information of a slave device is compared with the location information of a master device, and when it is determined that they are present in the same area, a warning release mode is set, and in the other case, a warning operation mode is set. The location information of the slave device when the warning release mode is changed to the warning operation mode is stored as reference location information, and the location information of the slave device is compared with the reference location information in the warning operation mode, and when it is determined that they are not in the same area, warning is outputted.