User equipment, comprising: a transmission and reception unit configured to transmit and receive a radio channel to/from a base station via multiple cells configured for carrier aggregation; a simultaneous transmission availability determination unit configured to determine, in response to occurrence of an event where an uplink control channel is to be transmitted in the multiple cells simultaneously, whether the uplink control channel can be transmitted in the multiple cells simultaneously; and a transmission control unit configured to: instruct the transmission and reception unit to transmit the uplink control channel in the multiple cells simultaneously if the uplink control channel can be transmitted in the multiple cells simultaneously; and control transmission of the uplink control channel in accordance with a transmission priority corresponding to a respective cell type of each of the multiple cells if the uplink control channel cannot be transmitted in the multiple cells simultaneously, wherein the transmission control unit has a cell type determination unit configured to determine which of a primary cell or a secondary cell the cell type of each cell is, and the transmission control unit is configured to control transmission of the uplink control channel in the determined cell corresponding to the determination in accordance with the transmission priority order of the primary cell and the secondary cell. a transmission and reception unit configured to transmit and receive a radio channel to/from a base station via multiple cells configured for carrier aggregation; a simultaneous transmission availability determination unit configured to determine, in response to occurrence of an event where an uplink control channel is to be transmitted in the multiple cells simultaneously, whether the uplink control channel can be transmitted in the multiple cells simultaneously; and a transmission control unit configured to: instruct the transmission and reception unit to transmit the uplink control channel in the multiple cells simultaneously if the uplink control channel can be transmitted in the multiple cells simultaneously; and control transmission of the uplink control channel in accordance with a transmission priority corresponding to a respective cell type of each of the multiple cells if the uplink control channel cannot be transmitted in the multiple cells simultaneously, instruct the transmission and reception unit to transmit the uplink control channel in the multiple cells simultaneously if the uplink control channel can be transmitted in the multiple cells simultaneously; and control transmission of the uplink control channel in accordance with a transmission priority corresponding to a respective cell type of each of the multiple cells if the uplink control channel cannot be transmitted in the multiple cells simultaneously, wherein the transmission control unit has a cell type determination unit configured to determine which of a primary cell or a secondary cell the cell type of each cell is, and the transmission control unit is configured to control transmission of the uplink control channel in the determined cell corresponding to the determination in accordance with the transmission priority order of the primary cell and the secondary cell.