A transmission device including a multi-division optical modulator having a plurality of modulation segments, the transmission device includes a driver circuit configured to output binary data for each bit based on an input electrical signal, and an optical modulator configured to have a multilevel modulation segment driven by a first drive signal including two or more bit signal from the driver circuit, and plural binary modulation segments driven by second drive signal including only one bit signal from the driver circuit, wherein the multilevel modulation segment incudes a first phase shifter disposed on each arm of the optical modulator, the binary modulation segment includes a plurality of second phase shifters arranged along each arm of the optical modulator, and lengths of the second phase shifters are all the same and are shorter than a length of the first phase shifter.