A color detecting sensor includes a light emitting element for emitting red light, a light emitting element for emitting green light, a light emitting element for emitting blue light, a light receiving element for receiving light emitted from each of the light emitting elements through an ink ribbon, and detecting device for detecting a color of the ink ribbon forming at least a colorless and transparent portion and the colorless and transparent portion based on an output signal of the light receiving element, the detecting device including a storage section for storing, as color reference data, the output signal of the light receiving element when the light emitting elements emit light through the colorless and transparent portion of the ink ribbon respectively, and a color deciding section for comparing, with the color reference data, the output signal of the light receiving element when the light emitting elements emit light through the color formed on the ink ribbon respectively, thereby deciding the color of the ink ribbon.