An image forming apparatus comprising: an image carrier having a surface on which a toner image is formed; a rotating brush coming into contact with the surface of the image carrier and then collecting a residue adhering to the surface after transferring the toner image to a transfer sheet; a collecting roller coming into contact with the rotating brush on a downstream side in a rotating direction of the rotating brush from a contact area between the image carrier and the rotating brush and then removing the residue collected by the rotating brush; and a cleaning blade abutting against the collecting roller on a downstream side in the rotating direction of the collecting roller from a contact area between the rotating brush and the collecting roller and then scraping the residue collected by the collecting roller, a sealing member having an extension part extending outside from each end of the collecting roller in an axial direction, and coming into contact with the collecting roller between the contact area between the rotating brush and the collecting roller and the cleaning blade and then preventing backflow of the residue; and a side sealing member configured to lift the extension part toward the collecting roller on an outside at a predetermined interval from a position corresponding to each side edge of a maximum-width sheet passing region on the image carrier, wherein a lower half of the sealing member is fixedly attached to an attachment plate supported by a supporting member and the sealing member is supported so as to come into contact with the collecting roller at a predetermined pressing force from an upstream side in the rotating direction of the collecting roller, the extension part can be lifted so as to come closer to the collecting roller by a predetermined distance with the side sealing member. an image carrier having a surface on which a toner image is formed; a rotating brush coming into contact with the surface of the image carrier and then collecting a residue adhering to the surface after transferring the toner image to a transfer sheet; a collecting roller coming into contact with the rotating brush on a downstream side in a rotating direction of the rotating brush from a contact area between the image carrier and the rotating brush and then removing the residue collected by the rotating brush; and a cleaning blade abutting against the collecting roller on a downstream side in the rotating direction of the collecting roller from a contact area between the rotating brush and the collecting roller and then scraping the residue collected by the collecting roller, a sealing member having an extension part extending outside from each end of the collecting roller in an axial direction, and coming into contact with the collecting roller between the contact area between the rotating brush and the collecting roller and the cleaning blade and then preventing backflow of the residue; and a side sealing member configured to lift the extension part toward the collecting roller on an outside at a predetermined interval from a position corresponding to each side edge of a maximum-width sheet passing region on the image carrier, wherein a lower half of the sealing member is fixedly attached to an attachment plate supported by a supporting member and the sealing member is supported so as to come into contact with the collecting roller at a predetermined pressing force from an upstream side in the rotating direction of the collecting roller, the extension part can be lifted so as to come closer to the collecting roller by a predetermined distance with the side sealing member.