An illumination device comprising: a light source configured to emit source light; a fluorescence generating unit configured to generate fluorescent light by use of the source light from the light source as excitation light, the fluorescent light having a longer wavelength than the source light; a wavelength selecting unit comprising a first segment and a second segment, the first segment allowing the source light to pass therethrough, and the second segment reflecting the source light while allowing the fluorescent light to pass therethrough, wherein the wavelength selecting unit disposes one of the first and second segments on the light paths of the source light and the fluorescent light alternately as time passes; a polarization converting unit disposed in a light path between the light source and the wavelength selecting unit and configured to convert polarization of light between linear polarization and circular polarization such that a first linear polarization component input thereto is converted into circular polarization and circular polarization input thereto is converted into a second linear polarization component perpendicular to the first linear polarization component; and a light guiding unit disposed in a light path between the light source and the polarization converting unit and configured to guide the first linear polarization component of the source light from the light source and the fluorescent light arriving from the fluorescence generating unit to the polarization converting unit and to guide the second linear polarization component of the source light arriving from the polarization converting unit to the fluorescence generating unit, wherein, when the first segment is placed in the light path, the source light from the light source travels through the light guiding unit, the polarization converting unit, and the first segment of the wavelength selecting unit in sequential order for output as first illumination light, and wherein, when the second segment is placed in the light path, the source light from the light source travels through the light guiding unit and the polarization converting unit to the wavelength selecting unit, and is then reflected by the second segment of the wavelength selecting unit to travel through the polarization converting unit and the light guiding unit to the fluorescence generating unit, which generates the fluorescent light traveling through the light guiding unit, the polarization converting unit, and the second segment of the wavelength selecting unit in sequential order for output as second illumination light, the second illumination light being output in a same direction as the first illumination light. a light source configured to emit source light; a fluorescence generating unit configured to generate fluorescent light by use of the source light from the light source as excitation light, the fluorescent light having a longer wavelength than the source light; a wavelength selecting unit comprising a first segment and a second segment, the first segment allowing the source light to pass therethrough, and the second segment reflecting the source light while allowing the fluorescent light to pass therethrough, wherein the wavelength selecting unit disposes one of the first and second segments on the light paths of the source light and the fluorescent light alternately as time passes; a polarization converting unit disposed in a light path between the light source and the wavelength selecting unit and configured to convert polarization of light between linear polarization and circular polarization such that a first linear polarization component input thereto is converted into circular polarization and circular polarization input thereto is converted into a second linear polarization component perpendicular to the first linear polarization component; and a light guiding unit disposed in a light path between the light source and the polarization converting unit and configured to guide the first linear polarization component of the source light from the light source and the fluorescent light arriving from the fluorescence generating unit to the polarization converting unit and to guide the second linear polarization component of the source light arriving from the polarization converting unit to the fluorescence generating unit, wherein, when the first segment is placed in the light path, the source light from the light source travels through the light guiding unit, the polarization converting unit, and the first segment of the wavelength selecting unit in sequential order for output as first illumination light, and wherein, when the second segment is placed in the light path, the source light from the light source travels through the light guiding unit and the polarization converting unit to the wavelength selecting unit, and is then reflected by the second segment of the wavelength selecting unit to travel through the polarization converting unit and the light guiding unit to the fluorescence generating unit, which generates the fluorescent light traveling through the light guiding unit, the polarization converting unit, and the second segment of the wavelength selecting unit in sequential order for output as second illumination light, the second illumination light being output in a same direction as the first illumination light.