US Patent 8123317 Ink tank and printing apparatus

To implement an ink tank and a printing apparatus that can detect a residual quantity of ink in an ink containing part optically with high accuracy by solving a problem of false detection of an ink residual quantity caused by irregular reflection light and scattered light generated by light from a light emitting part. For that purpose, the light source for emitting light of a first wavelength and the light receiving part for receiving light of a second wavelength are provided. Then the light of the first wavelength from the light source is configured to be irradiated on a luminescent material that is provided in the ink tank and emits the light of the second wavelength using an optical prism only when the ink does not exist in the ink tank.