A user apparatus is provided. The user apparatus communicates with a base station in a mobile communication system. The mobile communication system supports carrier aggregation which includes multiple cells including a first cell and a second cell which uses a TTI different from a TTI of the first cell. The user apparatus includes a communication unit configured to transmit and receive a signal to and from the base station; and a timer control unit configured to, according to a type of a control operation performed by the communication unit, determine a TTI as a unit time for operating a timer used for the control operation. The communication unit performs the control operation by operating the timer by using as a unit time the TTI determined by the timer control unit.