PURPOSE: To reduce greatly signal lines from respective detecting elements and to facilitate extremely fine adjustments, and further to secure a position detection by providing a potentiometer successively to the movement path of a moving body.

CONSTITUTION: The potentiometer 14 is provided in parallel to the movement path of a platen 1 to detect a movement position. A potentiometer 13 is off an image formation part and powered on by a power source 15. Then, the platen 1 is provided with a conductive brush 16 with an insulating member in-between and the brush 16 contacts the potentiometer 14 electrically. Therefore, the movement of the platen 1 allows the brush 16 to slide on the potentiometer, so that the voltage developed at the brush 16 varies with the movement. The movement of the platen 1 is transduced into the voltage by the potentiometer 14 and the voltage is led out through the brush 16.