A change of a magnetic flux density distribution adjacent to a regulating blade 9 opposed to a developer regulation pole is suppressed at a low cost, while suppressing influence to design latitude of magnetic poles. A position on the outer peripheral surface of the developing sleeve where the magnetic flux density in the normal line direction of the outer peripheral surface of the developing sleeve is a maximum value position. The position on the outer peripheral surface of the developing sleeve 8 corresponding to a center portion position of the half peak range of the magnetic flux density distribution of the developer regulation pole is called half peak center portion. The developer regulation pole is formed such that the maximum value position is deviated not less than 3° in the circumferential direction of the developing sleeve from the half peak center portion position, and the position when the regulating blade 9 opposite is the developing sleeve is in a side of the maximum value position in which the half peak center portion position exists.