An image forming device that is capable of performing transfer of paper
constantly in a highly accurate manner, irrespective of types or
conditions of paper. The image forming device is provided with a motion
sensor in a paper transfer path thereof for detecting the surface
condition of an idle roller moving in accordance with the paper, and
transfer of the paper is controlled on the basis of surface condition
signals generated by the motion sensor. The motion sensor makes laser
light, which is irradiated by a semiconductor laser, hit on an outer
peripheral surface of the idle roller that rotates accompanying the
transfer of paper and the reflected light is received by a
two-dimensional semiconductor image sensor. Then, the surface condition
signals are detected on the basis of speckle patterns generated in the
reflected light.