Developing agent storage device and image forming apparatus having same in which the chargeability level of the toner, storage device, and carrier have a specific relationship

An image forming apparatus, comprising:

• a latent image carrier configured to form a latent image;
• a development unit configured to develop the latent image formed on the latent image carrier using a developing agent;
• a developing agent refill device configured to refill the development unit with a developing agent, an amount of refilling developing agent being substantially equal to an amount of developing agent consumed in the development unit;
• a developing agent storage device configured to store refill developing agent to be supplied to the development unit, the developing agent storage device being detachably mountable to the developing agent refill device, the developing agent storage device including:
• toner particles, composing the refill developing agent;
• carrier particles, composing the refill developing agent;
• and
• an inner layer of the developing agent storage device, provided as a wall contacting the refill developing agent,
• wherein an electrostatic chargeability level of the toner particles, carrier particles, and inner layer is set in an increasing electrostatic chargeability level order of toner, inner layer, and carrier from a negative charge side or positive charge side.