An optical transmission system for optimizing the bias of a laser diode during an SCM analog optical transmission includes an optical transmitter for converting a baseband electric signal into an optical signal using a laser diode according to the set bias and outputting the optical signal through an optical line, an optical receiver for converting the optical signal transmitted from the optical transmitter into the baseband electric signal, a recovery unit for detecting an error generated according to the bias of the laser diode on the basis of the electric signal converted by the optical receiver, and a bias adjuster for optimally adjusting the bias of the laser diode on the basis of a value of the error detected by the reproducer.