A developing device has: a developer housing chamber in which developer is housed; a developer holding member holding developer by magnetic force; a partitioning wall having an overlapping region that, in a transparent plan view, is positioned upward of the developer holding member and overlaps the developer holding member in an up/down direction; and an opening portion formed in the overlapping region of the partitioning wall. The partitioning wall is a portion of a separating wall of the developer housing chamber, and is provided between the developer housing chamber and the developer holding member.