An optical recording/reproducing apparatus and a method therefor, and more particularly, an auto laser diode power controlling apparatus for controlling the power of a laser diode to be in an optimal state and a method therefor are provided. The auto laser diode power controlling apparatus for controlling the output of a laser diode by comparing the current power level of an optical signal output by the LD with a reference power level and controlling the output of the LD according to the comparison result comprises a photo detector (PD) (214) for monitoring the current power level of the optical signal output by the LD, a sampler/holder (202) for sampling and holding the current power level output from the PD, a sampling and holding control signal generator (208) for generating a sampling and holding control signal for controlling the sampling operation of the sampler/holder (202) on the basis of a non return to zero inverted (NRZI) signal, and an operator (204) for comparing the current power level sampled by the sampler/holder with the reference power level and controlling the output of the LD according to the difference value. It is possible to improve recording and reproducing performance since rapid change in an optical output is appropriately controlled using different loops according to the kind and state of the disc.