To provide a clean room structure used in an assembly process of a projector, capable of being rapidly installed in response to a market request, and of preventing inflow of contaminated air into a clean room from a pre-cleanroom.

In this clean room structure 10 for an assembly process of a projector, the clean room 20 has a blower device 22A or the like for supplying air into the clean room 20 by positively introducing the air from the outside and removing foreign matter, and an exhaust device 24 for exhausting air more than the blast amount of the blower device 22A or the like; the pre-cleanroom 40 has a first air passage 44 having a first filter 44a for introducing air from the outside by an atmospheric pressure difference from the outside and removing foreign matter; and a second air passage 28 for freely passing the air between the clean room 20 and the pre-cleanroom 40 is arranged in the vicinity of the first air passage 44.

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