A developer supply device configured to supply developer is provided. The developer supply device includes a rotatable developer carrying body configured to carry the developer, a casing configured to rotatably support the developer carrying body, and a restricting member configured to contact the developer carrying body to remove a part of the developer. The casing has a collecting side developer storage room configured to store the developer removed by the restricting member and a supplying side developer storage room configured to store the developer to be supplied to the brush layer. A supplying side developer storage level, which is a storage level of the developer in the supplying side developer storage room, is higher than a collecting side developer storage level, which is a storage level of the developer in the collecting side developer storage room.