A developer supply device is provided, which includes a transfer board including an activating section and an always-transferring section. The activating section is disposed in a position close to a developer holding member and lower than a position where development agent is transferred onto the developer holding member. The activating section is supplied with an activating voltage for making the development agent leave a developer transfer path and drop into the developer storage section during an activating process performed at an initial stage of a developer transferring operation while supplied with the transfer bias voltage after the activating process. The always-transferring section is disposed across a position facing the developer storage section to a position lower than and adjacent to the activating section, and always supplied with a transfer bias voltage during the developer transferring operation.