A transmission device includes: a plurality of modulators (13-1 to 13-4) that respectively generate multicarrier signals from given data; a distributor (12) that distributes input data to the modulators; an optical circuit (14-1 to 14-4, 15) that multiplexes the multicarrier signals to generate a WDM optical signal; and a controller (16) that obtains allocation information from a receiver of the WDM optical signal and generates a distribution instruction to control the distributor and a bit allocation instruction to control the modulators according to the allocation information. The allocation information is calculated based on transmission characteristics of each subcarrier of the respective multicarrier signals and the allocation information indicates a number of bits of data allocated to each of the subcarriers. The distributor distributes the input data to the modulators according to the distribution instruction. The modulators respectively allocate data distributed from the distributor to the subcarriers according to the bit allocation instruction to generate the multicarrier signals.