an image density controlling device for an image formation apparatus includes a plurality of image formation devices . a plurality of transfer members carry an image formed by at least one of the plurality of image formation devices . a belt rotates synchronously with the operation of the image formation devices and carries the transfer members . the belt includes a plurality of transfer member carrying areas on which the plurality of the transfer members are respectively carried , and a plurality of non - carrying areas therebetween . a density detection toner image is formed in the non - carrying area by utilizing at least one of the plurality of image formation devices . the density of the density detection toner image is determined to output a density detection signal . the densities of the images transferred to the transfer members are then controlled in accordance with the density detection signal . the density detection toner image formed in each rotation cycle of the belt is cleaned off and formed again at a different position of the belt .