A developer according to the present invention is arranged such that the composition of particulate metal oxide added as an external additive to a toner surface and the composition of particulate metal oxide added to a resin layer covering a carrier surface are identical to each other, so that the amount of frictional charge that is generated between the toner and the external additive is made larger than the amount of frictional charge that is generated between the external additive and the carrier surface. With this, the external additive is prevented from migrating from the toner surface onto the carrier surface. This makes it possible to prevent the external additive from migrating from the toner surface onto the carrier surface, and thereby to remedy (i) defects in charge and fluidity and (ii) secondary failures, i.e., defects in development that are caused by deterioration in performance of the developer due to the defects in charge and fluidity.