Developing device having thickness regulation blade

A developing device comprising:

• a casing;
• a developing roller rotatably supported to the casing and defining an axis extending in an axial direction, the developing roller being configured to rotate in a rotational direction and to carry a layer of developer thereon;
• a resiliently deformable blade supported to the casing and extending in the axial direction, the blade having a first surface facing the developing roller and a second surface opposite to the first surface, the blade having one axial end portion formed with a through-hole;
• a regulation portion configured to be in contact with the developing roller to regulate a thickness of the layer of the developer carried on the developing roller;
• and
• a covering portion provided on the second surface and positioned to cover the through-hole, wherein the covering portion extends to a distal end of the one axial end portion.