A 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 by carrier aggregation; a simultaneous transmission availability determination unit configured to, in response to an occurrence in the user equipment of an event to transmit an uplink control channel in the multiple cells simultaneously, determine whether the uplink control channel can be simultaneously transmitted by the user equipment in the multiple cells; and a transmission control unit configured to, if the uplink control channel can be simultaneously transmitted by the user equipment in the multiple cells, instruct the transmission and reception unit to transmit the uplink control channel in the multiple cells simultaneously, and if the uplink control channel cannot be simultaneously transmitted by the user equipment in the multiple cells, control transmission of the uplink control channel in accordance with a transmission priority, wherein the transmission control unit includes a carrier aggregation type determination unit configured to determine which of intra-eNB carrier aggregation or inter-eNB carrier aggregation is applied, and the transmission control unit sets the transmission priority depending on the determination, and the transmission control unit is configured to assign a relatively large amount of transmit power to an uplink control channel having the high transmission priority and assigns a relatively small amount of transmit power to an uplink control channel having the low transmission priority or stops the transmission. a transmission and reception unit configured to transmit and receive a radio channel to/from a base station via multiple cells configured by carrier aggregation; a simultaneous transmission availability determination unit configured to, in response to an occurrence in the user equipment of an event to transmit an uplink control channel in the multiple cells simultaneously, determine whether the uplink control channel can be simultaneously transmitted by the user equipment in the multiple cells; and a transmission control unit configured to, if the uplink control channel can be simultaneously transmitted by the user equipment in the multiple cells, instruct the transmission and reception unit to transmit the uplink control channel in the multiple cells simultaneously, and if the uplink control channel cannot be simultaneously transmitted by the user equipment in the multiple cells, control transmission of the uplink control channel in accordance with a transmission priority, wherein the transmission control unit includes a carrier aggregation type determination unit configured to determine which of intra-eNB carrier aggregation or inter-eNB carrier aggregation is applied, and the transmission control unit sets the transmission priority depending on the determination, and the transmission control unit is configured to assign a relatively large amount of transmit power to an uplink control channel having the high transmission priority and assigns a relatively small amount of transmit power to an uplink control channel having the low transmission priority or stops the transmission.