An optical recording medium master disc exposure apparatus comprises a modulating means 3 for modulating intensity of light from an exposure light source 1 in response to recording information and a focusing optical system 9 for focusing the light modulated by this modulating means 3 on a photoresist 12 on an optical recording medium master disc 11 to thereby pattern-expose the photoresist 12 in response to recording information. The exposure light source 1 is composed of a ultrashort wave pulse laser with a repetitive frequency of an integral multiple ranging from 1 time to 20 times as high as the clock frequency of recording information. This optical recording medium master disc apparatus includes an external synchronizing mechanism to vary the resonator length of this ultrashort wave pulse laser to mode-lock the repetitive frequency of the ultrashort wave pulse laser in synchronism with the clock frequency to cause the ultrashort wave pulse laser to emit pulses, and hence miniscule pits can be formed with high accuracy.