A developing device includes: a first frame; a second frame; a developer-carrying member; and a thickness-regulating member. The first frame includes: a pair of first walls opposed with each other; and a second wall connecting the pair of first walls and having a first fixing part. The second frame includes a third wall opposed to the second wall and attached to the pair of first walls when assembled to the first frame. The developer-carrying member has an axis extending in a first direction, is configured to rotate about the axis, and is disposed between the pair of first walls. The thickness-regulating member is fixed to the first fixing part and is configured to regulate a thickness of developer carried on the developer-carrying member. The third wall is disposed between the second wall and the thickness-regulating member.