A radio terminal unit and a radio communication system, enabling power savings, the improvement of the quality of real-time communication such as voice communication, and the reduction of transmission delays which often occur when a plurality of radio terminal units are connected to one radio base station. A radio terminal unit comprises an operation mode of communication application determination unit for determining operation mode of one or more communication which is operated at the radio terminal unit, a control packet changing unit for changing a timing of transmission of the control packet according to the operation mode of one or more communication applications determined by the operation mode of communication application determination unit, and a communication control section for sending the control packet according to the timing of transmission changed by the control packet changing unit after the transmission of data from the application.