To successively and accurately detect toner residual amount from a state where toner is full until a state where it is used up.

By providing two devices, that is, an optical system developer residual amount detecting device detecting the toner residual amount inside a developer container 17 by transmitting light through the container 17 and receiving the light transmitted through the container 17, and an antenna system developer residual amount detecting device detecting the toner residual amount inside the container 17 by providing an antenna electrode 13 near the container 17 and detecting the electrostatic capacity of the toner existing between a developing roller 3 and the electrode 13, the toner residual amount is detected by using the antenna system developer residual amount detecting device while the toner residual amount is 100% to 50% and using the optical system developer residual amount detecting device when the toner residual amount is ≤50%.