An optical modulation apparatus that performs optimum bias voltage control for optical modulation without using a pilot tone. A drive unit generates a drive signal by adding a bias voltage to an input data signal. A light modulation unit modulates input light output from a light source unit, in accordance with the drive signal, and outputs the results as optical signals. A forward monitoring unit monitors a forward signal of the light modulation unit and outputs the forward signal. A reverse monitoring unit monitors a reverse signal of the light modulation unit and outputs a reverse signal. A bias control unit controls the bias voltage so that a measured monitor ratio matches a target value of the ratio between the forward signal and the reverse signal, obtained when the operating point of the light modulation unit is in a predetermined position on its operation characteristic curve.