To provide an optical transmitter module with simplified control of a voltage to be applied to an optical modulator. An optical transmitter module includes a semiconductor laser for irradiating a laser beam; a demultiplexer for branching the laser beam to output branched light beams; optical modulators for modulating an optical amplitude of each of the branched light beams into a first optical amplitude or a second optical amplitude, depending on an input level at two levels; and a multiplexer for multiplexing output light beams from the optical modulators. The optical transmitter module may include optical waveguides for connecting the optical modulators and the multiplexer, and the optical waveguides may include a first optical waveguide for causing a first phase difference and a second optical waveguide for causing a second phase difference different from the first phase difference.