To provide an optical transmitting device which reduces mixed modulation caused by third distortion and suppresses the deterioration of service life by using an inexpensive semiconductor laser device.

Average power P0 of an input signal is detected by an envelope detector 5, and a bias driving current controller 6 outputs a bias driving current I0 which increases as the power P0 increases. The semiconductor laser device comprising a light emitter 4 is driven by a driving current superimposing the bias driving current I0 and a current signal (i) proportional to the input signal, and the strength of output light is modulated and the light is outputted to an optical cable 7. Therefore, when the power of the input signal increases, the bias driving current is increased and the influence of the non-linear distortion of the semiconductor laser device is reduced. When the power decreases, the bias driving current is decreased and the deterioration of the semiconductor laser device is prevented.