An image forming apparatus, comprising: a rotatable image carrier configured to carry a toner image developed with toner on a surface of the image carrier; a rotatable transfer member (33, 36) configured to form a transfer nip by contacting the image carrier surface; and a power supply configured to: output a voltage to transfer the toner image formed on the image carrier surface to a recording material captured in the transfer nip, and alternately switch the voltage between a voltage in the transfer direction to transfer the toner image from the image carrier to the recording material and a voltage opposite to the voltage in the transfer direction when the toner image formed on the image carrier surface is transferred to the recording material; wherein a time average value Vave of the voltage has a polarity of the transfer direction to transfer the toner image from the image carrier to the recording material and is set to a value closer to the transfer voltage side, and the image forming apparatus has a mode to change a cycle of the voltage output from the power supply based on toner information indicating a state of deterioration of the toner, characterized in that: a frequency of the alternating voltage is increased as the toner deteriorates; and the image forming apparatus is configured to change the cycle of the voltage by changing a frequency of the voltage output from the power supply based on a determined toner deterioration or by changing a processing linear velocity of the rotatable member (33, 36) of the image forming apparatus. a rotatable image carrier configured to carry a toner image developed with toner on a surface of the image carrier; a rotatable transfer member (33, 36) configured to form a transfer nip by contacting the image carrier surface; and a power supply configured to: output a voltage to transfer the toner image formed on the image carrier surface to a recording material captured in the transfer nip, and alternately switch the voltage between a voltage in the transfer direction to transfer the toner image from the image carrier to the recording material and a voltage opposite to the voltage in the transfer direction when the toner image formed on the image carrier surface is transferred to the recording material; wherein a time average value Vave of the voltage has a polarity of the transfer direction to transfer the toner image from the image carrier to the recording material and is set to a value closer to the transfer voltage side, and the image forming apparatus has a mode to change a cycle of the voltage output from the power supply based on toner information indicating a state of deterioration of the toner, characterized in that: a frequency of the alternating voltage is increased as the toner deteriorates; and the image forming apparatus is configured to change the cycle of the voltage by changing a frequency of the voltage output from the power supply based on a determined toner deterioration or by changing a processing linear velocity of the rotatable member (33, 36) of the image forming apparatus. output a voltage to transfer the toner image formed on the image carrier surface to a recording material captured in the transfer nip, and alternately switch the voltage between a voltage in the transfer direction to transfer the toner image from the image carrier to the recording material and a voltage opposite to the voltage in the transfer direction when the toner image formed on the image carrier surface is transferred to the recording material; wherein a time average value Vave of the voltage has a polarity of the transfer direction to transfer the toner image from the image carrier to the recording material and is set to a value closer to the transfer voltage side, and the image forming apparatus has a mode to change a cycle of the voltage output from the power supply based on toner information indicating a state of deterioration of the toner, characterized in that: a frequency of the alternating voltage is increased as the toner deteriorates; and the image forming apparatus is configured to change the cycle of the voltage by changing a frequency of the voltage output from the power supply based on a determined toner deterioration or by changing a processing linear velocity of the rotatable member (33, 36) of the image forming apparatus. a frequency of the alternating voltage is increased as the toner deteriorates; and the image forming apparatus is configured to change the cycle of the voltage by changing a frequency of the voltage output from the power supply based on a determined toner deterioration or by changing a processing linear velocity of the rotatable member (33, 36) of the image forming apparatus.