In the case of radio base stations of different kinds, a synchronization in a radio section cannot be established so that the efficiently effective use of electric waves cannot be retained. According to the invention, therefore, there is provided a TDMA type mobile communication system 100 comprising: a plurality of radio base stations of different system kinds (i.e., a general type radio base station 1, an IP connection type radio base station 10 and a main digital cordless phone 2); mobile phones 5A and 5B wirelessly connected with the plural radio base stations; and a private branch exchange 4 wired with the radio base stations. The radio base station receives, when a synchronized operation mode is decided, a frame signal containing a control CH signal, from a reference radio base station (i.e., a reference station); and times the transmission of the frame signal of a local station to the transmission position of the control CH signal in the frame signal, thereby to establish a frame synchronization in a radio section between own station and the reference radio base station.