An image forming apparatus includes a rotatable image bearing member, a nip forming member, and a power source. The rotatable image bearing member bears a toner image on a surface thereof and rotates. The nip forming member contacts the surface of the image bearing member to form a transfer nip therebetween. The power source applies a transfer bias to the transfer nip to transfer the toner image from the image bearing member onto a recording medium interposed in the transfer nip. The transfer bias includes a superimposed transfer bias in which an alternating current (AC) component is superimposed on a direct current (DC) component and a polarity of the superimposed transfer bias changes with time. A phase difference between an AC voltage and an AC current output from the power source is equal to or less than 0.47 cycles.