An optical transmission device includes a first detector, a generator, a second detector, and a controller. The first detector detects optical output power of an optical signal for each channel for input to a Mach-Zehnder unit that has asymmetric optical waveguides. The generator superimposes, based on the detected optical output power for each of the channels, a dither signal onto an optical signal in a specific channel from among the plurality of channels for input to the Mach-Zehnder unit. The second detector detects an amplitude value of the dither signal superimposed onto the optical signal in the specific channel output from the Mach-Zehnder unit. The controller adjusts a phase difference in the Mach-Zehnder unit such that the amplitude value of the dither signal superimposed onto the detected optical signal in the specific channel is less than a predetermined threshold.