An apparatus for optical master disk exposure for exposing guide grooves and pre-pits with laser beams has a reference signal generator which generates a reference signal for being supplied to a groove reference voltage generator that generates a groove reference voltage according to the reference signal. A pre-pit designation signal generator generates a pre-pit designation signal designating formation of the pre-pits. A pre-pit region voltage generator generates a pre-pit region voltage with a power of level of 70 to 75% of the groove reference voltage according to the pre-pit designation signal. A bias voltage generator generates a bias voltage with a power level of 80 to 90 of the groove reference voltage when no pre-pit is formed according to the pre-pit designation signal. A guide groove exposure voltage supplier adds together the groove reference voltage, the pre-pit region voltage and the bias voltage and outputs a guide groove exposure voltage to a laser beam modulating means which modulates the laser beams according to the guide groove exposure voltage received from the guide groove exposure voltage supplier. The guide grooves are uniformly formed thereby enabling the reduction of cross-talk.