A filter unit (300) includes: a chassis (303) that has a suction portion (301) provided at a front side thereof, has an exhaust portion (302) provided at a rear side thereof, and is provided internally with an upstream filter (331); a plurality of upstream first ribs (323) disposed parallel to sidewalls of the chassis (303) to rise from a bottom surface (322) of the chassis (303) and forming an upstream first airflow path (P11); a plurality of upstream second ribs (313) disposed parallel to the sidewalls of the chassis (303) to rise from a ceiling surface (312) of the chassis (303) and forming an upstream second airflow path (P21); an upstream first shield plate (315) raised from the ceiling surface (312) to cover up a front of the upstream filter (331) while forming an upstream first gap (S11) with the bottom surface (322); and an upstream second shield plate (325) raised from the bottom surface (322) to cover up a rear of the upstream filter (331) while forming an upstream second gap (S21) with the ceiling surface (312).