A polarization multiplexing optical transmitter of the present invention includes frequency dividing means (21) that performs frequency dividing on a clock signal having a Baud rate frequency, phase modulation means (8) that performs phase modulation on a light signal in accordance with the clock signal having undergone the frequency dividing, branching means (2) that branches the phase-modulated light into two light signals, delay means (10) that delays one branched light signal relative to the other branched light signal to generate light signals having phases inverted relative to each other, and polarization multiplexing means (5) that synthesizes the generated signals lights with orthogonal polarizations to generate a polarization multiplexed signal. Hence, the polarization multiplexing optical transmitter that can further improve the signal quality can be accomplished.