In an image reading device having a sheet-through mechanism, a controller controls a stepping motor to decelerate an image reading system when the image reading system is moved to a reference white plate reading position, and controls a stepping motor drive electric current to decrease when the image reading system reads a reference white plate. When the image reading system finishes reading the reference white plate, the controller controls the stepping motor drive electric current to increase so as to rapidly decelerate the image reading system. The controller further controls the stepping motor such that a moving speed of the image reading system to an original document reading position is lower than a moving speed of the image reading system to the reference white plate reading position.