A wavelength-swept light source apparatus comprises a light source that emits a wavelength-swept light that varies in a predetermined cycle, a mode hop detector that detects a mode hop of the wavelength-swept light emitted from the light source； and a control unit that controls at least one of a parameter that defines a specified period having a predetermined fixed or variable time length provided in the predetermined cycle and a control parameter of the light source, thereby to set an occurrence timing of the mode hop detected by the mode hop detector outside of the specified period. The wavelength-swept light source is used as input light source for an interferometric measuring system. In one embodiment the mode hop detector and the detector of the interferometric signal are the same detector.
