Image forming apparatus

An image forming apparatus, comprising:

• an image bearer to bear a toner image on a surface thereof;
• a transfer device to contact the image bearer to form a transfer nip;
• and
• a power source to output a voltage to transfer the toner image from the image bearer onto a recording medium interposed in the transfer nip, the voltage including a first voltage in a transfer direction in which the toner image is transferred from the image bearer to the recording medium and a second voltage having a polarity opposite that of the first voltage, and the first voltage and the second voltage alternating upon transfer of the toner image from the image bearer to the recording medium;
• wherein the power source is configured to output the voltage that is superimposed with a plurality of the alternating current voltages having a waveform of at least one of the following:
• sine, triangular, and rectangular, and
• wherein a waveform of the voltage is biased in the transferring direction.