A transmission device includes a wavelength multiplexer that wavelength-multiplexes a plurality of optical signals having different wavelengths to generate a wavelength-multiplexed optical signal, an amplifier that outputs the wavelength-multiplexed optical signal to a transmission path, and a first processor that allocates wavelength bands to the plurality of optical signals to be wavelength-multiplexed into the wavelength-multiplexed optical signal and controls power of the wavelength-multiplexed optical signal in accordance with the wavelength bands allocated to the plurality of optical signals.