Abstract: It is difficult to carry out automatic bias control to an optical modulator without a dither signal with a simple configuration, therefore, an optical transmitter comprising the controller configured to adjust an adjusted bias voltage based on the coupled optical signal, the adjusted bias voltage being one of a first bias voltage applied to the first optical modulator, a second bias voltage applied to the second optical modulator and a third bias voltage applied to the third optical modulator and maintain a value of bias voltages other than the adjusted voltage in the first bias voltage, the second bias voltage and the third voltage.