To provide a modular building capable of omitting works involved in assembly and construction as much as possible so as to be constructed easily and at a low cost.

A modular building is provided with a plurality of hut units 16 obtained by dividing a hut 11 portion in the vertical direction, and a plurality of foundation units 31c, 31d composing a foundation 31 portion. The plurality of hut units 16 and the plurality of foundation units 31c, 31d are produced in a factory in advance and conveyed to a construction site. The plurality of foundation units 31c, 31d are connected to each other at their end parts in the construction site to form the foundation 31 portion, and the plurality of hut units 16 are connected onto the foundation 31 portion formed by the plurality of foundation units 31c, 31d.