A power saving mode is provided. A method for entering a power saving mode of a terminal includes a first operation for starting a first timer after transmitting an idle mode request message; a second operation for, when an idle mode approval message is not received until the first timer expires, checking whether a number of retransmissions of the idle mode request message exceeds a number of allowed retransmissions of the idle mode request message; a third operation for, when the number of the retransmissions of the idle mode request message exceeds the number of the allowed retransmissions of the idle mode request message, increasing a number of idle mode entry failures; and a fourth operation for, when the increased number of the idle mode entry failures is greater than N times, entering a power saving mode which powers off a modem.