A projector includes a case, a separating plate, an electronic component system, a light source device and a blocking device. The case has a space defined therein. The separating plate is arranged in the case to divide the space into a first space and a second space. The electronic component system is arranged in the first space. The light source device for emitting light is arranged in the second space. The blocking device has a blocking plate which is arranged adjacent to the separating plate and controlled to be located from a first position and a second position. When the blocking plate is located at the first position, air flows from the first space into the second space. When the blocking plate is located at the second position, air in the second space is prevented from entering into the first space.