If a configuration is employed in which modulation schemes used for an optical communication system can be switched depending on transmission conditions, it is difficult to make effective utilization of frequency resources without the power consumption increasing and the control becoming complex; therefore, an optical transmitter according to an exemplary aspect of the present invention includes an interface means for converting a digital signal to be transmitted under a predetermined transmission condition over an optical carrier wave into a parallel signal with a predetermined bit number at a predetermined transmission rate, and outputting the parallel signal; an encoding means for encoding the parallel signal using one coding system from among a plurality of convolutional coding systems with different degrees of redundancy; a mapping means for mapping an output bit signal output from the encoding means to a modulation symbol; an optical modulation means for modulating the optical carrier wave based on a symbol signal output from the mapping means; and an encoding control means for selecting a predetermined coding system corresponding to the predetermined transmission condition from among the plurality of convolutional coding systems and controlling the interface means, the encoding means, the mapping means, and the optical modulation means in such a way as to operate in accordance with the predetermined coding system.