PURPOSE: To realize the control of toner replenishment with high accuracy by forming the toner image corresponding to a reference density pattern on a photosensitive body and adjusting the rate of toner replenishment according to the ratio between the light reflectivity thereof and the light reflectivity of a photosensitive body surface.

CONSTITUTION: The densities of the toner image of the reference density pattern and the photosensitive body itself are measured at; for example, every 10 times of copying process and the contents of a flag Ftr and counter TN are set according to the results of the measurement. The toner replenishment, is, therefore, executed respectively in subsequent 5 times of copying processes when the flag Ftr set at 1 and 5 is set at the counter TN as the result of the density measurement. Ten times of the recording processes are set in the control cycle for the toner replenishment in the above-mentioned manner and the toners of the respectively specified amts. are replenished from a toner replenishing means in N-times of the respective recording processes among 10 times. The value of the parameter N is adjusted according to the ratio of the light reflectivity of the photosensitive body surface and the light reflectivity of the toner image of the reference density pattern. The control of the developer concn. with the high accuracy is thereby realized.