A mobile communication system according to the present invention includes: a radio base station for transmitting and receiving the electromagnetic waves of a circuit switching type radio communication system and the electromagnetic waves of a packet switching type radio communication system; and a communication terminal including an antenna for transmitting and receiving the electromagnetic waves of the circuit switching type radio communication system and the electromagnetic waves of the packet switching type radio communication system, a tracking unit for directing the orientation of the antenna to an arrival direction of the electromagnetic waves, a receiver for demodulating the electromagnetic waves of the circuit switching type radio communication system and the electromagnetic waves of the packet switching type radio communication system which are received, a transmitter for modulating the contents to be transmitted into the electromagnetic waves of the circuit switching type radio communication system and the electromagnetic waves of the packet switching type radio communication system, a handset for indicating predetermined information to the exterior and receiving an instruction from the exterior, and a controller for controlling the above respective units and implementing an initial acquiring procedure from which a tracking procedure or the like is omitted when a predetermined condition is satisfied, for example, at the time of switching from the circuit switching type radio communication system to the packet switching type radio communication system. Accordingly, a period of time required when switching the radio communication systems can be reduced.