Optical transmitter and method for controlling bias for optical modulator

An optical transmitter includes a signal generator configured to generate a drive signal from input data, an optimal modulator configured to have a voltage-to-light-intensity characteristic in which intensity of output light changes in response to an applied voltage, and to generate a light signal that corresponds to the drive signal, a multiplier configured to multiply the drive signal and an electric signal that is obtained from the light signal; and a control section configured to control based on output of the multiplier, a bias voltage for the optical modulator.