To provide a clean room building which can implement a production room having a large span space with high damping properties even if it does not have large cross-sectional floor framing.

The clean room building 1 is comprised of the production room 2 formed of a clean room, and an auxiliary room 3 arranged immediately below the production room 2. Then, a core column 4 is arranged at the planar center of the auxiliary room 3, which bears the floor framing 5 of the production room 2, and a horizontal force resistant frame 8 is arranged on the periphery of both the production room 2 and the auxiliary room 3. The core column 4 has an elevation installation (clean lifter 7) installed therein, for connecting the production room 2 and the auxiliary room 3 to each other.