An optical modulation circuit including: a continuous light source; an optical multicarrier generation unit; an optical dividing unit; an optical modulation unit (4-1 to 4-n); an optical combining unit; and a modulator drive signal generation unit; wherein the continuous light source is adapted to generate continuous light with a constant power, the optical multicarrier generation unit is adapted to generate optical multicarriers having n, n≥2, different frequencies with phase synchronization based on the continuous light from the continuous light source, where n is an integer, the optical dividing unit is adapted to divide the optical multicarriers from the optical multicarrier generation unit for each of the n different frequencies to output n optical carriers, the optical modulation circuit being characterized in that: the modulator drive signal generation unit is adapted to modulate data to be transmitted into n modulator drive signals so that the optical modulation unit generates a total of n ∗ (m+m) optical subcarriers which have m, m≥1, and m, m≥1, in total, m+m, different frequencies respectively before and after each of the frequencies of the n optical carriers from the optical dividing unit and on which different data is superimposed, the optical modulation unit is adapted to modulate the n optical carriers from the optical dividing unit into the total of n ∗ (m+m) optical subcarriers using the n modulator drive signals, and the optical combining unit is adapted to combine the total of n ∗ (m+m) optical subcarriers output from the optical modulation unit, the symbol rate of the optical subcarriers equals to the distance between the optical subcarriers, and the optical multicarrier generation unit comprises a phase-shift modulator and an intensity modulator which are serially connected and driven with synchronized clock signals. a continuous light source; an optical multicarrier generation unit; an optical dividing unit; an optical modulation unit (4-1 to 4-n); an optical combining unit; and a modulator drive signal generation unit; wherein the continuous light source is adapted to generate continuous light with a constant power, the optical multicarrier generation unit is adapted to generate optical multicarriers having n, n≥2, different frequencies with phase synchronization based on the continuous light from the continuous light source, where n is an integer, the optical dividing unit is adapted to divide the optical multicarriers from the optical multicarrier generation unit for each of the n different frequencies to output n optical carriers, the optical modulation circuit being characterized in that: the modulator drive signal generation unit is adapted to modulate data to be transmitted into n modulator drive signals so that the optical modulation unit generates a total of n ∗ (m+m) optical subcarriers which have m, m≥1, and m, m≥1, in total, m+m, different frequencies respectively before and after each of the frequencies of the n optical carriers from the optical dividing unit and on which different data is superimposed, the optical modulation unit is adapted to modulate the n optical carriers from the optical dividing unit into the total of n ∗ (m+m) optical subcarriers using the n modulator drive signals, and the optical combining unit is adapted to combine the total of n ∗ (m+m) optical subcarriers output from the optical modulation unit, the symbol rate of the optical subcarriers equals to the distance between the optical subcarriers, and the optical multicarrier generation unit comprises a phase-shift modulator and an intensity modulator which are serially connected and driven with synchronized clock signals. the modulator drive signal generation unit is adapted to modulate data to be transmitted into n modulator drive signals so that the optical modulation unit generates a total of n ∗ (m+m) optical subcarriers which have m, m≥1, and m, m≥1, in total, m+m, different frequencies respectively before and after each of the frequencies of the n optical carriers from the optical dividing unit and on which different data is superimposed, the optical modulation unit is adapted to modulate the n optical carriers from the optical dividing unit into the total of n ∗ (m+m) optical subcarriers using the n modulator drive signals, and the optical combining unit is adapted to combine the total of n ∗ (m+m) optical subcarriers output from the optical modulation unit, the symbol rate of the optical subcarriers equals to the distance between the optical subcarriers, and the optical multicarrier generation unit comprises a phase-shift modulator and an intensity modulator which are serially connected and driven with synchronized clock signals.