A developing device includes: a casing; a developing roller rotatably supported to the casing; a resiliently deformable blade supported to the casing; a regulation portion; and a covering portion. The developing roller is rotatable in a rotational direction and carries a layer of developer thereon. The blade extends in an axial direction of the developing roller and has one axial end portion formed with a through-hole, the blade having a first surface facing the developing roller and a second surface opposite to the first surface. The regulation portion is configured to be in contact with the developing roller to regulate a thickness of the layer of the developer carried on the developing roller. The covering portion is provided on the second surface and positioned to cover the through-hole.