An illumination device and an observation system capable of outputting light having a continuous spectrum and high color rendering properties are provided. Employed is an illumination device including a first light source that emits first-wavelength-band light having a first wavelength band of violet color; a second light source that emits second-wavelength-band light having a second wavelength band that is broader than the first wavelength band and having a continuous spectrum; a light combining section that is composed of a dicroic mirror and that combines the first-wavelength-band light and the second-wavelength-band light; and a combination-ratio adjusting section that adjusts the combination ratio of the first-wavelength-band light and the second-wavelength-band light to be combined by the light combining section.