PURPOSE: To obtain an electrophotographic printing machine where a print need not be monitored by an operator and the density of a pattern is stable and surface staining is not caused.

CONSTITUTION: In the electrophotographic printing machine provided with a photosensitive drum 1, an electrostatic charger 4, an exposure device 5, a developing electrode roller 7, a squeezing roller 8 and a transfer device, an infrared detector 12 which detects the toner film thickness and the solvent film thickness of the surface of the drum 1 provided on the downstream side of the roller 8, a means 18 which calculates the toner film thickness based on the toner film thickness signal of the detector 12, the means 18 which arithmetically compares the calculated toner film thickness with set toner film thickness which is previously inputted, a means 16 which controls the voltage of the roller 7 based on the calculated result, a means 13 which calculates the concentration of developer based on the solvent film thickness signal of the detector 12 and the means 13 which arithmetically compares the calculated concentration of the developer with set concentration which is previously inputted and a means which controls the speed of the revolution of the roller 8 based on the calculated result are provided.