A development unit includes: a developing vessel in which a developing agent is received; a developing member as defined herein; a supply member which is supported in the developing vessel and disposed to be opposed to the developing member, the supply member rotating the developing agent in the developing vessel while holding the developing agent on a surface of the supply member to thereby supply the developing agent held on the surface to the developing member; and a thickness limiting member as defined herein, and the supply member is supported movably in a direction to expand or reduce a gap between the thickness limiting member and the supply member so that the gap between the thickness limiting member and the supply member can be adjusted.