CLAIMS 1. A communication system, comprising:
a communication terminal device; and
a base station device configuring at least one cell capable of radio communication with said communication terminal device,
wherein said communication terminal device includes a narrow-bandwidth terminal device that performs radio communication at a bandwidth narrower than a system bandwidth that can be used by said cell,
said narrow-bandwidth terminal device performs discontinuous reception for intermittently receiving a signal transmitted from said cell and determines a reception condition of said signal when said narrow-bandwidth terminal device is in an idle state within a coverage area of said cell, and
said narrow-bandwidth terminal device moves out of said coverage area of said cell while continuing to perform said discontinuous reception, when said reception condition of said signal satisfies a predetermined moving condition.
2. The communication system according to claim 1,
wherein said moving condition is a determination that said signal cannot be received.
3. The communication system according to claim 1,
wherein said moving condition is a determination that a reception quality of said signal is lower than or equal to a predetermined moving threshold.
4. The communication system according to one of claims 1 to 3,

wherein said narrow-bandwidth terminal device performs a cell selection process upon completion of a period of said discontinuous reception after moving out of said coverage area of said cell.
5 5. The communication system according to one of claims 1 to 3,
wherein said narrow-bandwidth terminal device performs a cell selection process before moving out of said coverage area of said cell, when said reception condition of said signal satisfies a predetermined moving condition.