A developer carrier (16) includes magnetic field generating means (25) provided with a plurality of magnetic poles including an agent separating pole (P4) and a scooping pole (P6), and a cylindrical hollow body (26) accommodating therein the magnetic field generating means (25) and rotated around an axis of the cylindrical hollow body. A half-value width of a magnetic flux density at both end portions of at least one magnetic pole of the agent separating pole (P4) and the scooping pole (P6) is formed to be identical to or narrower than a half-value width of the magnetic flux density at a central portion of the one magnetic pole.