Patent ID: 8639166

Claim:
A developer supply device comprising: a casing comprising: a developer storage section provided at a bottom portion therein; and an opening formed at an end thereof away from the developer storage section; powdery development agent chargeable with a predetermined polarity, stored in the developer storage section of the casing, the development agent comprising: a mother particle having, around an outer surface thereof, an electrically insulating layer without a polar group having a charge polarity identical to the predetermined polarity; and an external additive absorbed to around the mother particle in an easily desorbable manner, the external additive being an electrically insulating fine particle having a charge polarity identical to the predetermined polarity; and a transfer board disposed in the casing, the transfer board comprising a plurality of transfer electrodes arranged along a developer transfer path from developer storage section to the opening, the transfer board being configured to, when a multi-phase alternating-current voltage is applied to the plurality of transfer electrodes, transfer the development agent from the developer storage section toward the opening along the developer transfer path, so as to supply an intended device with the development agent charged with the predetermined polarity.