To provide an optical transmitter which is capable of normally detecting the light interruption of a main signal even in a small number of wavelengths and attaining acceleration and stable operation when initially starting a device.

The number of wavelengths in output light to an optical transmission line and the light power of each wavelength are detected by a spectrum analyzer 80, and a control section 81 controls the power of Super Continuum light 300 outputted to a high non-linearity fiber so as to settle the number of wavelengths and the light power within a prescribed range. In output beams from the high non-linearity fiber, a wavelength component corresponding to a signal beam is removed by a filter 70 and an output beam of the filter 70 and the signal beam are multiplexed by a photocoupler 50.

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