Patent ID: 7734229

Claim:
A toner replenishing method comprising: a concentration measurement step of measuring a concentration of toner in a housing portion in which is accommodated a dual-component developer composed of toner and a carrier; a consumption calculation step of determining an amount of toner consumption; a setting step of setting, based on the amount of toner consumption determined in the consumption calculation step, a variable reference concentration for replenishment of toner to the housing portion and variable replenishment extension time for continuing the replenishment of toner to the housing portion after the concentration of toner reaches the reference concentration; and a toner concentration adjustment step of starting the replenishment of toner to the housing portion when the concentration of toner measured in the concentration measurement step is found to be equal to or less than a predetermined replenishment starting concentration, and stopping the replenishment of toner to the housing portion at a time following a lapse of the replenishment extension time from a time at which the concentration of toner of less than the reference concentration reached the reference concentration.