Method and apparatus for image forming capable of effectively preventing toner adhesion on a density sensor by generating an electric field according to a visible image

An image forming apparatus includes an image bearing member configured to bear a visible image including a toner charged with a predetermined polarity, an intermediate transfer member configured to receive the visible image from the image bearing member during a primary transfer process before the visible image is transferred onto a transfer medium during a secondary transfer process, a sensor configured to detect a density of the visible image, and a supporting member configured to support the intermediate transfer member and to generate an electric field having a polarity opposite to the predetermined polarity of the toner, in which the supporting member is held in contact with the intermediate transfer member and facing the sensor with the intermediate transfer member interposed therebetween.