This invention provides a developer concentration adjustment apparatus, a method for concentration adjustment, and an image forming apparatus, in which concentration adjustment is performed by use of a stirring load as a substitute characteristic of viscosity which represents a developer concentration, wherein a trouble of abnormality generation in toner concentration detection due to drying-adhesion of a residual developer on the stirrer is reduced. At the time of finishing the concentration adjustment, a concentration adjustment tank is made to be empty and the stirrer is cleaned by carrier liquid or a liquid developer having a concentration lower than a predetermined concentration. Alternatively, the stirrer is cleaned by empty-stirring operation not being put in a cleaning developer.