A first carrying member supplies a developer to a developer carrier at the position of a developer attracting magnetic pole H4 while longitudinally carrying the developer, and a second carrying member carries the developer released from the developer carrier at the position of a developer releasing magnetic pole H3. The developer carrier 13a has two magnetic poles H2 and H4 of the same polarity sandwiching the developer releasing magnetic pole H3. Moreover, the developer releasing magnetic pole H3 is formed by the two magnetic poles H2 and H4 so that the polarity of the developer releasing magnetic pole H3 differs from the polarity of the two magnetic poles H2 and H4.