There is provided a developer that has excellent positive charging characteristics and charging stability, and which is compatible with high-speed developing. The developer of the invention contains toner particles and an insulating liquid, wherein a fatty acid ester is contained as the insulating liquid, a substance A expressed by the following formula (1) and/or a substance B expressed by the following formula (2) is further contained, and the total percentage in which substance A and substance B are contained is at least 0.1 wt % and no more than 3.0 wt %.