In an image forming mode in which, a first image forming portion forms a toner image on the first image bearing member and a second image forming portion does not form a toner image on the second image bearing member, thereby forming an image on a recording material, a first voltage smaller than a minimum value of absolute values of a plurality of voltages applied to a plurality of grid electrodes of the first image forming portion and larger than an absolute value of a target potential of a surface of the second image bearing member in the image forming mode is applied to one of the plurality of grid electrodes of the second image forming portion, and no voltage is applied to the other grid electrodes except the grid electrode to which the first voltage is applied among the plurality of grid electrodes of the second image forming portion.

In an image forming mode, in which a first image forming portion forms a toner image on a first image bearing member and a second image forming portion does not form a toner image on a second image bearing member, thereby forming an image on a recording material, a first voltage lower than a minimum value of absolute values of a plurality of voltages applied to a plurality of grid electrodes of the first image forming portion and higher than an absolute value of a target potential of a surface of the second image bearing member in the image forming mode is applied to one of a plurality of grid electrodes of the second image forming portion, and no voltage is applied to the other grid electrodes except the grid electrode to which the first voltage is applied among the plurality of grid electrodes of the second image forming portion.

An image forming apparatus includes four photosensitive members, a first optical scanning unit, a second optical scanning unit, a first detection unit, a second detection unit and a control unit. The first optical scanning unit draws a first reference image and a first opposite image. The second optical scanning unit draws a second reference image and draws a second opposite image. The first detection unit detects the internal temperature of at least one of the first optical scanning unit and the second optical scanning unit. The second detection unit detects an apparatus internal temperature within an apparatus main body. The control unit corrects positions of the drawing of the first opposite image, the drawing of the second reference image and the drawing of the second opposite image based on the amount of change in the internal temperature and the amount of change in the apparatus internal temperature.