A communication system including: a mobile station connectable to a first radio communication system and a second radio communication system which uses a different radio access technology from the first radio communication system and uses a plurality of frequency bands; and a communication control device configured to control switching of the mobile station from the first radio communication system to the second radio communication system, characterized in that the communication control device comprises a switching instruction transmission unit configured to transmit to the mobile station a switching instruction which gives an instruction to switch from the first radio communication system to the second radio communication system and an indication on a plurality of switching target frequencies included in the frequency bands used by the second radio communication system, wherein the switching instruction transmission unit transmits the switching instruction before acquisition of information relating to frequency bands in which the mobile station is capable of transmission/reception, and the mobile station comprises: a frequency band determination unit configured to determine frequency bands of the second radio communication system, which is redirection target, indicated in the switching instruction, and to pick out only frequencies of the frequency bands in which the mobile station is capable of transmission/reception, out of the frequency bands thus determined; a quality determination unit configured to search for only cells using the frequencies included in the frequency bands picked out by the frequency band determination unit and to determine cells satisfying a prescribed reception quality threshold, and a connection target cell processing unit configured to determine a cell for connection with the mobile station among the cells satisfying the prescribed reception quality threshold. a mobile station connectable to a first radio communication system and a second radio communication system which uses a different radio access technology from the first radio communication system and uses a plurality of frequency bands; and a communication control device configured to control switching of the mobile station from the first radio communication system to the second radio communication system, characterized in that the communication control device comprises a switching instruction transmission unit configured to transmit to the mobile station a switching instruction which gives an instruction to switch from the first radio communication system to the second radio communication system and an indication on a plurality of switching target frequencies included in the frequency bands used by the second radio communication system, wherein the switching instruction transmission unit transmits the switching instruction before acquisition of information relating to frequency bands in which the mobile station is capable of transmission/reception, and the mobile station comprises: a frequency band determination unit configured to determine frequency bands of the second radio communication system, which is redirection target, indicated in the switching instruction, and to pick out only frequencies of the frequency bands in which the mobile station is capable of transmission/reception, out of the frequency bands thus determined; a quality determination unit configured to search for only cells using the frequencies included in the frequency bands picked out by the frequency band determination unit and to determine cells satisfying a prescribed reception quality threshold, and a connection target cell processing unit configured to determine a cell for connection with the mobile station among the cells satisfying the prescribed reception quality threshold. a frequency band determination unit configured to determine frequency bands of the second radio communication system, which is redirection target, indicated in the switching instruction, and to pick out only frequencies of the frequency bands in which the mobile station is capable of transmission/reception, out of the frequency bands thus determined; a quality determination unit configured to search for only cells using the frequencies included in the frequency bands picked out by the frequency band determination unit and to determine cells satisfying a prescribed reception quality threshold, and a connection target cell processing unit configured to determine a cell for connection with the mobile station among the cells satisfying the prescribed reception quality threshold.