A developing device has a developer carrier, a regulating member, a regulating pole, and a magnetic pole generation member. The regulating member has a magnetic body for regulating the thickness of developer on the surface of the developer carrier. The regulating pole is arranged inside the developer carrier to face the regulating member. The magnetic pole generation member is arranged upstream of the regulating member in the developer carrier rotation direction, and has a magnet for generating, at an end portion of the regulating member, a magnetic pole of a polarity different from that of the regulating pole. The regulating member has, in its side face, a depressed portion having an inner face with an arc-shaped cross-section. The magnetic pole generation member is cylindrical, with a radius substantially equal to that of the inner face of the depressed portion, and is rotatable while staying fitted in the depressed portion.