Abstract: A method of assembling a large-size plant and an assembling method for reducing a term of work are disclosed. Each of a crane operator in a crane operation room and site workers in a plant construction site is equipped with a picture I/O device and a voice I/O device. The crane operator and the site workers assemble the plant while sharing picture information of the picture I/O device and voice information of the voice I/O device with each other. A site remote control room vicinal to the plant construction site is connected via a radio transmission path to a host control center. The plant si assembled while the site workers, the crane operator room, the site remote control room and the central control room share the picture information and the voice information of their own with each other.