Provided are an apparatus for and a method of generating millimeter waves, in which millimeter-wave generation and frequency up-conversion can be achieved at the same time using a single device. The apparatus includes a mode-locking laser diode (LD) which has a distributed feedback (DFB) sector and a gain sector and generates high-frequency optical pulses through a passive mode locking process, a modulator which modulates an external optical signal using an electric signal and injects the modulated optical signal to the mode-locking LD to lock the optical pulses, and a radio frequency (RF) locking signaling unit which injects the electric signal to the modulator.