An image forming apparatus includes an image bearer to bear a toner image, a toner image forming device to form the toner image on the image bearer, a nip forming device to contact the image bearer to form a transfer nip between the image bearer and the nip forming device, a transfer bias output device to output a transfer bias including a DC component and an AC component to transfer the toner image from the image bearer onto a recording medium interposed in the transfer nip, and a controller operatively connected to the transfer bias output device to adjust a frequency f of the AC component of the transfer bias in accordance with an image area ratio A such that the frequency f is at its minimum with a predetermined image area ratio Amin %, where Amin % is greater than 0 but lower than an image area ratio of a solid image.