Abstract: An apparatus and method for extending the service area in a mobile communication system is provided, in which the service area is defined with a normal mode or an extension mode based on a distance between the base station and the mobile station and, in case of the extension mode, a transmission clock used by the mobile station for transmitting signals is changed, thus extending the service area. The access is attempted in the normal mode, and the transmission clock for transmitting the mobile signal is advanced the initial delay in the extension mode when the access fails. The access is reattempted with repeating the control of the transmission clock until the number of times of the access attempt reaches a predetermined number of times. When the number of times of the access currently attempted is greater than the predetermined number of times, the extension mode is converted to the normal mode, returning to the initial state.