Toner and development unit and image forming apparatus using the same

A developing unit comprising:

• a toner;
• a toner carrier which carries said toner;
• and
• a member which contacts with said toner carrier via said toner,
• wherein said toner comprises:
• mother particles;
• and external additive particles to be attached to said mother particles, and includes mother particles having an external additive concentration not lower than a predetermined concentration and mother particles having an external additive concentration lower than a predetermined concentration,
• wherein said toner satisfies the following relationship:
• D1/D2<2
• wherein D1 represents the average of the equivalent particle sizes of the entire mother particles, and D2 represents the average of the equivalent particle sizes of said mother particles having an external additive concentration lower than a predetermined concentration.