The optical frequency comb generating device having two optical modulation parts 41 and 42 independently modulating optical waves propagating in two branch waveguides and a phase regulator 43 controlling a phase difference between the optical waves includes amplitude adjusting means 22 for adjusting a voltage amplitude of the RF signal supplied to at least one of the optical modulation parts, monitoring means 21 for monitoring the intensity Pout of the output light beam, and a bias control circuit 20 that controls the amplitude adjusting means to change a difference in voltage amplitude between the RF signals supplied to each optical modulation part, that detects a variation of the output light beam corresponding to the variation of the difference in voltage amplitude from the output signal of the monitoring means, and that controls the phase regulator on the basis of the detection result to adjust the phase difference.