A superposed image forming apparatus wherein toner images are superposedly transferred onto a transfer material includes an image bearing member; a device for forming a toner image on the image bearing member; a transfer material carrying member, disposed opposed to the image bearing member, for carrying a transfer material in synchronism with the toner image on the image bearing member; a transfer material supplying device for supplying the transfer material to the transfer material carrying member; a transfer bias voltage source for applying to the transfer material carrying member a bias voltage for image transfer from the image bearing member to the transfer material; an attraction member for urging the transfer material to the transfer material carrying member to hold the transfer material on the transfer material carrying member; an attraction bias voltage source for applying a bias voltage to the attraction member; the bias voltage applied to the attraction member is changed in association with on-and-off of the bias voltage application to the transfer material carrying member so as to maintain a constant surface potential of the transfer material carrying member.
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