To provide an image forming apparatus equipped with a developing apparatus having a residual developer quantity detecting means using an optical fiber and an optical fiber holding member.

In an image forming apparatus equipped with the developing apparatus having a function of detecting the residual developer quantity, the apparatus is provided with the residual developer quantity detecting means constituted of an optical fiber 10 for transmitting light emitted from a light emitting part 14 arranged in the image forming apparatus body to a light receiving part 15 arranged in the same image forming apparatus body, and optical fiber holding members 11, 12 and 13 for holding the optical fiber 10, and the surfaces of the optical fiber holding members 11 and 13 are formed in a curved shape 11a so as to uniformly diffuse the light.