PURPOSE: To compensate excellent print quality irrelevantly to the thickness and structure of a printing medium and to reduce the amount of ozone which is produced by corona discharge by providing a control part which operates according to a printing medium kind signal and controls the operating current of a separation charger.

CONSTITUTION: A printing medium kind detecting means 7 which detects the kind and thickness of the printing form 3 and sends the printing medium kind signal is arranged by a printing medium supply means 4 and the control part 8 which receives the printing medium kind signal and controls the current for operating the separation character 6 is mounted. Consequently, the excellent print quality is secured irrelevantly to the thickness and structure of the printing form and the amount of ozone which is produced by the corona discharge is reduced to preclude environmental destruction.