An optical transmitter includes, an optical modulator that multilevel-modulates light outputted from a light source, and a processor that outputs a first drive voltage for driving the optical modulator according to an amplitude component when transmission data is symbol-mapped and a second drive voltage for driving the optical modulator according to a phase component when the transmission data is symbol-mapped. A phase shift of phase modulation by the second drive voltage outputted from the processor is greater than 0 and less than π/2.