An object of the present invention is to provide a radio communication system capable of effectively coping with the two problems, which are in a trade-off relation between the deterioration of the use efficiency of the radio resources and the deterioration of the radio quality of the secondary cell, in the cases where both a combination of carrier frequency bands that are away from each other and a combination of carrier frequency bands that are adjacent to each other can be alternatively used as the combination of carrier frequency bands for a primary cell and a secondary cell. A radio communication system according to the present invention includes a mobile station (20), and a base station (10) configured to perform radio communication with the mobile station (20) by using first and second carrier frequency bands simultaneously for at least one of an uplink direction and a downlink direction. Further, the mobile station (20) and the base station (10) are configured to be able to switch whether or not to perform control relating to the second carrier frequency band by using a radio channel transmitted on the second carrier frequency band.