Disclosed is a method of controlling a transition to an idle mode in an operation method for transitioning to an idle mode in a wideband wireless communication system, including: receiving an unsolicited deregistration response message including an action code instructing the terminal to transmit a deregistration request message for a transition to an idle mode and deregistration request message transmission time information from a base station; extracting control information in which a poll bit for reporting whether or not a message has been received is set from the received unsolicited deregistration response message; transmitting a deregistration request message including response information with respect to the extracted control information and a deregistration request code for requesting a transition to an idle mode, to the base station; and receiving a deregistration response message including an action code permitting a transition to an idle mode.