A filter unit, for use in an image forming apparatus that transfers a toner image to a recording medium to form an image, comprising: a rectangular parallelepipedic chassis that has a suction portion provided at a front side thereof to suck air therethrough, has an exhaust portion provided at a rear side thereof to exhaust the air therethrough, and is provided internally with a filter (331, 332) capable of collecting powder particles, characterized in that the filter unit further comprising: a plurality of first ribs (323, 324) disposed parallel to sidewalls (311, 321) of the chassis to rise from a bottom surface of the chassis toward an interior of the chassis and forming a first airflow path (P11, P12); and a plurality of second ribs (313, 314) disposed parallel to the sidewalls (311, 321) of the chassis to rise from a ceiling surface of the chassis toward the interior of the chassis and forming a second airflow path (P21, P22), wherein the filter (331, 332) is disposed in the interior of the chassis so as to be sandwiched by the plurality of first ribs (323, 324) and the plurality of second ribs (313, 314) while leaving spaces between the filter (331, 332) and the ceiling and bottom surfaces (312, 322), and wherein the filter unit further comprises: a first shield plate (315, 316) that extends in a direction perpendicular to a direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the ceiling surface of the chassis toward the interior of the chassis to cover up a front end of the filter (331, 332) while forming a first gap with the bottom surface of the chassis; and a second shield plate (325, 326) that extends in the direction perpendicular to the direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the bottom surface of the chassis toward the interior of the chassis to cover up a rear end of the filter (331, 332) while forming a second gap with the ceiling surface of the chassis. the filter unit further comprising: a plurality of first ribs (323, 324) disposed parallel to sidewalls (311, 321) of the chassis to rise from a bottom surface of the chassis toward an interior of the chassis and forming a first airflow path (P11, P12); and a plurality of second ribs (313, 314) disposed parallel to the sidewalls (311, 321) of the chassis to rise from a ceiling surface of the chassis toward the interior of the chassis and forming a second airflow path (P21, P22), wherein the filter (331, 332) is disposed in the interior of the chassis so as to be sandwiched by the plurality of first ribs (323, 324) and the plurality of second ribs (313, 314) while leaving spaces between the filter (331, 332) and the ceiling and bottom surfaces (312, 322), and a plurality of first ribs (323, 324) disposed parallel to sidewalls (311, 321) of the chassis to rise from a bottom surface of the chassis toward an interior of the chassis and forming a first airflow path (P11, P12); and a plurality of second ribs (313, 314) disposed parallel to the sidewalls (311, 321) of the chassis to rise from a ceiling surface of the chassis toward the interior of the chassis and forming a second airflow path (P21, P22), wherein the filter (331, 332) is disposed in the interior of the chassis so as to be sandwiched by the plurality of first ribs (323, 324) and the plurality of second ribs (313, 314) while leaving spaces between the filter (331, 332) and the ceiling and bottom surfaces (312, 322), and wherein the filter unit further comprises: a first shield plate (315, 316) that extends in a direction perpendicular to a direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the ceiling surface of the chassis toward the interior of the chassis to cover up a front end of the filter (331, 332) while forming a first gap with the bottom surface of the chassis; and a second shield plate (325, 326) that extends in the direction perpendicular to the direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the bottom surface of the chassis toward the interior of the chassis to cover up a rear end of the filter (331, 332) while forming a second gap with the ceiling surface of the chassis. a first shield plate (315, 316) that extends in a direction perpendicular to a direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the ceiling surface of the chassis toward the interior of the chassis to cover up a front end of the filter (331, 332) while forming a first gap with the bottom surface of the chassis; and a second shield plate (325, 326) that extends in the direction perpendicular to the direction of extension of the first ribs (323, 324) and the second ribs (313, 314) and is raised from the bottom surface of the chassis toward the interior of the chassis to cover up a rear end of the filter (331, 332) while forming a second gap with the ceiling surface of the chassis.