Circulation system for an image developer with an agitator motor responsive to an amount of developer in a storage tank

A developer circulation system, comprising:

• a storage tank which stores a developer including a carrier liquid and a toner;
• a development device which carries out a development process using the developer supplied from the storage tank;
• a developer supply passage through which the developer is supplied to the development device from the storage tank;
• a developer return passage through which the developer is returned to the storage tank from the development device;
• a circulation pump which supplies the developer in the storage tank to the development device via the developer supply passage, the circulation pump also returns the developer in the development device to the storage tank via the developer return passage;
• and
• an agitation member which agitates the developer in the storage tank, wherein
• an outlet of the developer return passage and an opening of the developer supply passage are located in the storage tank, so as to promote a flow of the developer generated by the rotation of the agitation member, at positions furthest from each other along a flow of the developer from the outlet of the developer return passage and the opening of the developer supply passage,
• a level sensor which measures an amount of the developer in the storage tank;
• an agitation motor which rotates the agitation member;
• and
• a control unit which adjusts a rotation speed of the agitation motor to different levels of the rotation speed in accordance with the amount of the developer in the storage tank which is measured by the level sensor.