An optical transmitter includes an optical modulator including a first modulator, a second modulator, and a phase shifter that provides a predetermined optical phase difference between the first modulator and the second modulator, a light source that makes light enter the optical modulator, and a voltage controller that detects a distortion of light power characteristics from output light of the optical modulator in a state where no data signal is input to the optical modulator to determine a bias voltage to be set in the optical modulator while reducing the distortion.