Abstract: A locking apparatus for an optical frequency multiplex system, including a local oscillating unit for applying low frequency signals to individual light sources and thereby making center frequencies of the light sources dither, photocouplers for grouping dithering optical signals outputted from the light sources into a single signal, a resonator for aligning the signals coupled by the photocouplers with optical frequency slots, respectively, a photodetector for converting a reflection optical signal from the photocouplers into a current signal, and an optical frequency stabilizing controller for controlling the light sources on the basis of an error signal detected by the photodetector, whereby the error signal is extracted using the reflection output rather than the transmitting output of the resonator, thereby being capable of enhancing the extinction ratio and maximizing the number of multiplexing light sources.