A developing device having a developing gap detecting function includes a photosensitive
medium, a developer conveyer, a DC power source, an AC power source, a current
detecting unit and a controller. The current detecting unit detects a DC current
flowing on the developer conveyer when toner from the developer conveyer is attached
to a desired area of an electrostatic latent image on a photosensitive body by
enhancing a voltage outputted from a power supply gradually at proper intervals.
The controller obtains a developing gap between the photosensitive medium and the
developer conveyer based on current values detected by the current detecting unit.
In accordance with the developing device having the developing gap detecting function,
the developing gap is sensed and developing voltage is easily and correctly calculated
to control image forming conditions. As a result, an image quality improves.