To provide a coating fluid for forming an undercoat layer having high stability, a high-quality and long-life electrophotographic photoreceptor for forming a high-quality image in various use environments and hardly inducing image defects such as black spots and color spots, an image forming apparatus using the photoreceptor, and an electrophotographic cartridge using the photoreceptor.

The coating fluid for forming an undercoat layer for an electrophotographic photoreceptor, the layer containing a binder resin and metal oxide particles formed on a conductive support is characterized in that: in a liquid prepared by diluting the coating fluid with a solvent mixture of methanol and 1-propanol in a weight ratio of 7:3, the difference between the absorbance to light having a wavelength of 400 nm and the absorbance to light having a wavelength of 1,000 nm is at most 1.0 (Abs) in the case that the refractive index of the metal oxide particles is at least 2.0. The electrophotographic photoreceptor has an undercoat layer formed by being coated with the coating fluid.

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