There is described an image forming apparatus equipped with a cleaning unit to clean a belt-type transfer member. The cleaning unit includes: a conductive opposing roller that contacts an inner surface of the intermediate transfer member; a first conductive brush member and a second conductive brush member, both of which are pressed against the conductive opposing roller while putting the intermediate transfer member between them; a cleaning-voltage applying power source to apply a cleaning voltage having a polarity opposite to that of the residual toner onto the first conductive brush member; and an opposing-roller potential controlling unit to control an electric potential state of the conductive opposing roller, so that an electric potential difference, between the first conductive brush member and the conductive opposing roller at a time when the secondary transferring unit is deactivated, is larger than that at a time when the primary transferring unit is activated.