There is provided a transmission apparatus configured to transmit an optical signal by using a plurality of subcarriers, the transmission apparatus includes: a plurality of modulators, a modulator of the plurality of modulators configured to be capable of changing a modulation format corresponding to a subcarrier of the plurality of subcarriers; a controller configured to control the modulation format for the modulator so as to use a first modulation format and a second modulation format for two or more subcarriers among the plurality of subcarriers and include subcarriers that are different in at least one of a first timing and a second timing of the first modulation format; and a multiplexer configured to multiplex signals modulated by the plurality of modulators.