Provided is a mobile communication system which includes a plurality of RAT (Radio Access Technology) and can eliminate the need of a control channel for reporting RAT information so as to prevent congestion or shortage of the control channel capacity. In the mobile communication system, an LTE relay station (30) has a cover area (31) identical to a cover area (21) owned by a WLAN host station (20) and relays/transmits the signal received from an LTE base station (10) to a mobile station (40) in the cover area (31). The LTE relay station (30) adds to the signal received from the LTE base station (10), one of the offsets: a frequency offset, a time offset, and a power offset as information indicating that the mobile station (40) which receives a relay signal from the local station is located in the cover area (21) of WLAN and transmits the signal after offset addition to the mobile station (40) located in the cover area (31) (i.e., the cover area (21)).