A light modulation apparatus including a Mach-Zehnder type light modulator, a driver for modulator outputting a control signal according to an input electric signal, a light branching circuit branching the output light signal, and a bias control circuit applying a bias voltage to the light modulator based on the branched light signal, the apparatus further comprises: a burst pause state detection circuit detecting a pause state of a burst signal included in the input electric signal; a photoelectric transducer converting an output light signal branched by the light branching circuit into an electric signal; a sampling circuit extracting the electric signal converted while the pause state is detected by the burst pause state; and a bias voltage adjustment circuit adjusting a bias voltage value of the bias voltage based on a voltage level of the extracted electric signal.