There is provided a wavelength variable light source system capable of changing wavelength and intensity of output signal light and of improving preset accuracy and stability of the wavelength and strength of the output signal light. The system determines the both or either one of a target value for controlling wavelength and a target value for controlling intensity of output signal light of a wavelength variable light source by correlating a combination of the target wavelength and the target light output intensity specified from a higher-level device and controls operation states of the wavelength variable light source so that output values of monitoring circuits for monitoring the operation state of the wavelength variable light source converge to the target values.