The image forming apparatus includes a first image bearing member, a movable second image bearing member, a charging device and a voltage applying device, wherein a toner image is transferred from the first image bearing member to the second image bearing member at a first transfer portion, the toner image is transferred from the second image bearing member to a transfer material at a second transfer portion, the charging device is opposed to the second image bearing member at a downstream side of the second transfer portion and at an upstream side of the first transfer portion with respect to a moving direction of the second image bearing member, the voltage applying device switches a DC voltage from a first voltage to a second voltage which is opposite in polarity to the first voltage, the switching from the first voltage to the second voltage is executed at every predetermined number of transfers of the toner image from the second image bearing member to the transfer material, and the predetermined number varies depending on an image forming condition.