An image forming apparatus comprising: an image forming unit configured to form a toner image on a recording material (P) by using toner containing a parting agent; a fixing unit provided with a first rotatable member and a second rotatable member , contacting said first rotatable member , configured to form a fixing nip portion for fixing the toner image on the recording material (P) by applying heat and pressure while feeding and nipping the recording material (P); a heating portion configured to heat said first rotatable member ; a duct in which a suction opening provided in a neighborhood of said fixing unit and an exhaust opening through which an air sucked from said suction opening is discharged; and a fan connected to said exhaust opening and configured to generate an air flow from said suction opening to said exhaust opening ; characterized by further comprising a sheet-like filter provided with a base layer and a collecting layer laminated on said base layer for collecting dust, and configured to cover said suction opening ; wherein when a downstream side of said filter with respect to a suction direction is inside and an upstream side of said filter with respect to the suction direction (Z) is outside, said filter is disposed so that said collecting layer is inside and said base layer is outside, and wherein in a cross section perpendicular to a longitudinal direction of said filter , a central portion of said filter in a widthwise direction is outside of an edge portion of said filter in the widthwise direction, and when a width of said suction opening in the widthwise direction is d1, a maximum height of said filter from an imaginary surface passing through an edge portion of said suction opening is L, said filter satisfies the following formula: 0.003 < L / d 1 < 5 . an image forming unit configured to form a toner image on a recording material (P) by using toner containing a parting agent; a fixing unit provided with a first rotatable member and a second rotatable member , contacting said first rotatable member , configured to form a fixing nip portion for fixing the toner image on the recording material (P) by applying heat and pressure while feeding and nipping the recording material (P); a heating portion configured to heat said first rotatable member ; a duct in which a suction opening provided in a neighborhood of said fixing unit and an exhaust opening through which an air sucked from said suction opening is discharged; and a fan connected to said exhaust opening and configured to generate an air flow from said suction opening to said exhaust opening ; characterized by further comprising a sheet-like filter provided with a base layer and a collecting layer laminated on said base layer for collecting dust, and configured to cover said suction opening ; wherein when a downstream side of said filter with respect to a suction direction is inside and an upstream side of said filter with respect to the suction direction (Z) is outside, said filter is disposed so that said collecting layer is inside and said base layer is outside, and wherein in a cross section perpendicular to a longitudinal direction of said filter , a central portion of said filter in a widthwise direction is outside of an edge portion of said filter in the widthwise direction, and when a width of said suction opening in the widthwise direction is d1, a maximum height of said filter from an imaginary surface passing through an edge portion of said suction opening is L, said filter satisfies the following formula: 0.003 < L / d 1 < 5 . <EOS>