PURPOSE: To charge a toner electrostatically and stably by friction with a carrier and to prevent the scattering of the toner by changing the replenishing ratio of the toner without changing the operating speed of a toner replenishing device according to the change in the compsn. of the developer.

CONSTITUTION: Two turning rollers 10a, 10b for replenishing are provided in the lower part of a hopper 9 which contains a toner in the inside assuming a funnel shape, and these are driven and controlled by means of a motor and a clutch. The roller 10a keeps revolving at all times during copying work to replenish the toner and the roller 10b is operated by the signal from a toner concn. detecting element 13 to replenish the toner. Fine grooves or small dents are provided on the surfaces of the rollers 10a, 10b, and the toner is carried out continuously by each small amt. from the hopper 9. Thereby, the toner is charged electrostatically and stably by friction with the carrier and the scattering of the toner is prevented.