An optical disc recording/reproducing apparatus and optimum bias power decision method thereof, having an optical pickup, a driving unit which drives a laser diode provided in the optical pickup to emit light corresponding to a certain bias power, a bias power variation unit which varies the bias power and outputs the varied bias power to the driving unit, and a bit error rate measurement unit which reproduces the recorded data, compares the reproduced data and the recorded data, and measures at least one bit error rate. A controller is further provided which calculates a relationship equation between the measured bit error rate and the varied and output bias power upon recording the data, and decides an optimum bias power based on at least one maximum value and at least one minimum value in a curve obtained from the relationship equation.