An image forming apparatus includes a first image bearing member, a movable second image bearing member, a charging device and a voltage applying device. A toner image is transferred from the first image bearing member to the second image bearing member at a first transfer portion, and 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 a 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.