To contrive shortening the construction period in a bypass tunnel electric precipitator used in a ventilation system of a road tunnel because the conventional system wherein an accessory chamber and an electric chamber which each are installations for surely operating main equipment of an electric precipitator and a blower have various pieces of equipment arranged and connected in airtight and solid buildings and for these chambers, after the bypass tunnel has completed, equipment and materials of the buildings are brought in and work is done before manufacturing work and inspection of equipment such as bringing-in, installation, wiring, piping, connection, and testing are performed has a drawback that the total construction period is prolonged.

Pieces of auxiliary equipment and pieces of power source equipment are classified by related function, and the classified pieces are disposed a container-shaped functional (containers 1-8, and work up to wiring, piping, and inspection is completed in specialty plants every functions, and at the same time with the completion of a bypass tunnel 101, the functional containers are brought in and arranged, and are made to communicate with each other by an airtight path, and connection of wiring and piping and passing of safety personnel can be also performed.