An image forming apparatus includes a latent image bearer to bear a plurality of halftone images having a same image density and a high-density image located one cycle downstream of the latent image bearer from at least one of the plurality of halftone images, a transferor to apply a predetermined transfer voltage to transfer the plurality of halftone images and the high-density image, a transfer electric field forming target to bear the plurality of halftone images and the high-density image transferred from the latent image bearer, a detector to detect image densities of the plurality of halftone images on the transfer electric field forming target, and a controller to determine a primary transfer voltage applied at a time of image formation, based on image density variations of the plurality of halftone images detected by the detector.