Abstract: A projector includes a housing, an internal projection mechanism, and an external air filtration device. The housing has a ventilation window portion. The internal projection mechanism is disposed in the housing, and includes an imaging system, a light source system for providing a light beam to the imaging system, and a ventilating fan. The external air filtration device includes a frame, a filter member, and an engaging unit. The engaging unit engages removably the frame to the ventilation window portion of the housing for securing the filter member on the exterior of the housing between the frame and the ventilation window portion.