PURPOSE: To facilitate adjusting operation and maintain a strict blade gap by providing projection members to a blade which limits the conveyance amount of a developer, and fixing the blade.

CONSTITUTION: The blade 5 is fitted to the front part of a toner box 3 and the blade gap H2 is adjusted through a long-sized hole 6 to regulate the amount of the developer conveyed on the peripheral surface 2a of a developing sleeve 2. The projection members 8 are provided at both end parts 5b of the blade 5 at distance from the napping area β of the developing sleeve 2, and project from the front edge 5a of the blade 5 by length corresponding to the blade gap H2. A stop screw 7 is only clamped while the protection members 8 are pressed against the peripheral surface 2a of the developing sleeve 2 to complete the adjusting operation speedily without using any gauge.