A power-down mode control apparatus includes an internal power-down control block configured to receive a locking completion signal and to generate an internal power-down signal, which is toggled for a predetermined time; a noise check block configured to check occurrence/non-occurrence of noise on the basis of a phase detection signal and to generate a plurality of power-down selection signals in response to the locking completion signal and the internal power-down signal; and a power-down enter control block configured to generate a plurality of power-down enter signals, which instruct individual circuits to enter a power-down mode in response to a reference clock signal, the plurality of power-down selection signals, a power-down mode signal, and the internal power-down signal.