A toner supplier apparatus 1 is provided for stabilizing the concentration of toner reserved in a main tank. A concentration sensor for measuring the concentration of the toner is provided in a toner-feeding pipeway for supplying liquid toner from a main tank for adjusting the concentration to the developer apparatus. High concentration toner and diluent supplied to the main tank are controlled based on the concentration measured by the concentration sensor. Accordingly, accuracy of the toner supplier apparatus used for an electronic photograph printer in measuring the concentration of the toner can be improved, thereby permitting accurate control for the concentration in a printed image.