PURPOSE: To enable progression and suppression of electric discharge by providing a grid for controlling space charge between a discharge wire and a screen grid.

CONSTITUTION: An electrostatic charger consists of a discharge wire 1, a grid 2 for controlling space charge, a screen grid 3 and an outside frame shield 4. The influence of temp. on the corona start voltage at paired flat plates of a positive needle having a determined gap is such that the corona discharge voltage decreases as the temp. rises. The discharge gap length optimum for the electrophotographic process is therefore taken larger than the discharge gap length l1 shown in the figure and the impressed voltage is taken larger than the corona discharge voltage of a dotted line to meet said gap. If the corona start voltage increases with a decrease in temp., the voltage of the same polarity as the polarity of the voltage impressed to the wire 1 is impressed to the grid 2 and the substantially large voltage is kept impressed to the wire 1. The voltage on the grid 2 is changed in conformity with the temp. detecting circuit. The corona start is thus progressed by decreasing the voltage of the grid 2 when the temp. is low, and the corona start is suppressed by increasing the voltage when the temp. is high. The stable discharge hence stable charging characteristics is obtd.