A transmission method includes mapping a data signal to a symbol according to a modulation mode to generate a first electric field signal and a second electric field signal, modulating a light beam based on the first electric field signal and the second electric field signal to generate a first polarized light beam and a second polarized light beam that are orthogonal to each other, multiplexing the first polarized light beam and the second polarized light beam, applying transformation processing of changing each polarization angle of the first polarized light beam and the second polarized light beam to the first electric field signal and the second electric field signal and adding polarization information indicating a change amount caused by the transformation processing for each polarization angle of the first polarized light beam and the second polarized light beam to the first electric field signal and the second electric field signal.