To provide a space partition structure of a unit building, in which a partition device for partitioning an indoor space can be suitably installed.

First, second and third building units 20a, 20b and 20c are juxtaposed in the building 10, and a habitable room space 31 in a first floor section is formed of the building units 20a-20c. The habitable room space 31 is formed, as a continuous space, of a first habitable room space 31a possessed by the first building unit 20a, a second habitable room space 31b possessed by the second building unit 20b, and a third habitable room space 31c possessed by the third building unit 20c. A screen device 40, which has a screen for partitioning the habitable room space 31 and a screen case for housing the screen, is provided in the ceiling of the first floor section. The screen case is arranged in a gap between ceiling girders of the building units 20 adjacent each other.