PURPOSE: To prevent a developer from scattering from an opening part which faces the photosensitive body of a developing device by providing an air flow guide plate along a developing roll from near a development part, and providing a discharge opening for air in the side wall of the air flow guide plate at a larger interval from the developing roll.

CONSTITUTION: The air flow guide plate 10 is provided along the downstream- side surface in the rotational direction of the developing roll 7 so that the distance increases gradually, and the discharge opening 11 for air is formed in the housing-side wall at a widened distance position. When the rotating sleeve 6 of the developing roll 7 rotates as shown by an arrow B, air flowing along the surface of the developing roll 7 does not flow into a developer 8 banking at the bottom part and the pressure in the space C of the bottom part rises, so that air flows out of the housing 2 through the discharge opening 11. Consequently, the air is sucked from outside of the housing near the opening part into the housing, so no developer scatters from the opening part.