Image forming apparatus providing constant toner level in developing unit

A process unit for use with an image forming apparatus, comprising:

• a drum unit comprising a photosensitive drum;
• and
• a developing unit being movable relative to the drum unit, the developing unit comprising:
• a frame comprising:
• a first chamber;
• a second chamber having an inlet opening through which toner is introduced to the second chamber, the second chamber and the first chamber being arrayed in a horizontal direction in a state where the process unit is attached to the image forming apparatus;
• an adjustment member positioned between the first chamber and the second chamber, the adjustment member being configured to adjust movement of the toner between the first chamber and the second chamber;
• a developing roller disposed in the first chamber;
• and
• a toner supply member disposed in the second chamber, the toner supply member comprising:
• a shaft rotatably supported by the frame, and
• a flexible sheet disposed on the shaft, the flexible sheet being configured to move while being in contact with the adjustment member when the shaft is rotating,
• wherein the adjustment member has a slit, the slit of the adjustment member having a width ranging from 0.5 mm to 5.0 mm for allowing the toner to pass therethrough from the second chamber to the first chamber.