In a configuration with a plurality of developing units, an influx of air into one developing unit from another developing unit can be blocked with a simple configuration. An operation section for a developing unit that is not in operation rotates a developer roll in the reverse direction to move developer accumulated on a pickoff pole, and fills a clearance formed between a housing and the developer roll with the developer so that the air flow of the developing unit that is not in operation is blocked. Accordingly, even if a difference in pressure between a developing unit that is in operation and a developing unit that is not in operation occurs, an air flow from the developing unit in operation to the developing unit not in operation is not apt to be formed, and an influx of air into the developing unit that is not in operation is blocked.