A developing device includes: a developing roller, a casing which rotatably supports the developing roller; a thickness regulation blade; and first and second holding members which fix the thickness regulation blade on the casing. The first holding member includes: a first nipping surface which contacts the thickness regulation blade; and a first fixing surface. The second holding member includes: a second nipping surface which opposes the first nipping surface; and a second fixing surface contacting the first fixing surface. The thickness regulation blade includes a positioning opening and is sandwiched between the first nipping surface and the second nipping surface. The first nipping surface includes a projection which is fitted into the positioning opening of the thickness regulation blade.