PURPOSE: To provide a printing engine generating pulse width modulating output driving a matrix printing head to print an image comprising a continuous line of dots changed in density on a moving image receiving medium.

CONSTITUTION: Bias voltage of 160 V is maintained across an image generating device (RIP) 10, a shaft encoder 18 and a printing engine 12 by an optical separator 22. The printing engine 22 is equipped with an ion ejection head 16, a dispersion type digital controller and analogue drive circuits 20a, 20b to raise the voltage of the ejection head 16. The controller 18 is constituted of a master controller and a finger controller and the image data from the image generating device 10 is distributed to the finger controller by the master controller. The writing of a line is synchronized to an induction cylindrical body 14 by the finger controller. Therefore, the ion ejection head 16 of the engine 12 is distributed by the dispersion type controller 18 to be operated to eject ions to a latent image receiver 14.