PURPOSE: To eliminate the influence of the variation of a photosensitive body by forming a titled device from a detecting electrode provided between a coronode and the photosensitive body, and a constant-voltage element installed between back electric conductors of the photosensitive body, detecting a current flowing through the constant- voltage element, controlling an output of a high voltage power source, and keeping the current constant.

CONSTITUTION: When the unevenness of an electrostatic charge is generated in a photosensitive body 6, a large current flows to a part whose potential is low since a potential difference between a grid 4 and the photosensitive body 6 is large, a current of a part whose potential is high is suppressed, and the unevenness is reduced. Also, when the position relation of a structure of a charger 1 and the photosensitive body 6, and a characteristic of a constant-voltage element 7 are constant, a current IV flowing through the constant-voltage element 7 is determined by the potential of the photosensitive body 6. Accordingly, to make the IV constant is to execute the same operation as to detect the charged potential of the photosensitive body 6 and to control it to a constant state. Accordingly, it is possible to detect and control the potential within the mounting range of a charger to reduce the cost of the device, and to be scarcely influenced by contamination, etc.