A developer unit according to one aspect of the invention includes: a developer accommodation member configured to accommodate a developer having charging polarity to a first polarity opposite to a second polarity; a developing roller arranged at the developer accommodation member, the developing roller being configured to carry the developer; a supply roller arranged at the developer accommodation member and configured to supply the developer to the developing roller, an image formation width being defined on a surface of the supply roller along an axis direction of the supply roller; and a charging member brought into sliding contact with an outside of the image formation width of the supply roller. The charging member at a portion brought into sliding contact with the supply roller is formed of a material which is positioned on a side of the second polarity on a triboelectric series relative to the supply roller.