Disclosed is an orthogonal frequency division multiplexing (OFDM) optical transmitter including a signal size adjustor for amplifying plural data signals modulated based on an OFDM scheme with different amplification rates so that each data signal is amplified according to a size of the corresponding data signal. Accordingly, it is possible to reduce a peak-to-average power ratio, and thus a nonlinear phenomenon generated in an optical line can be reduced and the quality of an OFDM optical signal can be improved.