An image forming apparatus includes an image bearing member for bearing a toner image, a rotatable intermediary transfer member onto which the toner image is to be primary-transferred from the image bearing member, a contact member movable toward and away from the intermediary transfer member, a voltage applying unit for applying a voltage to the contact member, a current detecting circuit for detecting a current passing through the contact member, and a control portion for effecting control so that the contact member is in contact with or separated from the intermediary transfer member. The control portion can operate a measuring mode in which a contact time required to bring the contact member into contact with the intermediary transfer member is calculated by applying an initial voltage to the contact member, then by outputting a contact instruction signal to move the contact member to be in contact with the intermediary transfer member, and then by measuring a time from output of the contact instruction signal until the current detecting circuit detects a predetermined current value.