Disclosed are a waste toner amount detecting apparatus and method which can detect whether a waste toner bottle is full of a waste toner using a change in a current of a motor which drives an auger, and an image forming apparatus employing the same. The waste toner amount detecting apparatus is in an image forming apparatus which includes a motor current detector to detect a drive current of a motor which rotates an auger for leveling the waste toner contained in the waste toner bottle; and a controller which includes a determining unit to determine whether the waste toner bottle is full of the waste toner, using a difference between a first current value corresponding to a minimum drive current of the motor and a second current value corresponding to a current drive current of the motor.