A dummy-light generating device includes a continuous wave (CW) light source that outputs CW light, a modulated-light generating unit that generates, using the CW light, first intensity-modulated light subjected to intensity modulation and second intensity-modulated light delayed by a half time of a modulation cycle of the first intensity-modulated light with respect to the first intensity-modulated light and having a polarization state e different from a polarization state e of the first intensity-modulated light, and a polarization combiner that performs polarization combination of the first intensity-modulated light and second intensity-modulated light and outputs light after the polarization combination as dummy light.