PURPOSE: To eliminate retardation of installation of component parts and facilitate change of the coating color by installing a coated outer board to a chassis constituent body, on which component parts can be installed, from the outside using a color fastening tool.

CONSTITUTION: A chassis constituent body 2 is constructed by combining angle members by means of welding etc., wherein four columns 22-25 are installed upright at the four corners of a bottom plate 21, and a table frame 27 is erected at a level in the middle between the columns. Also a cross-sash 28 is installed in the space to the columns 23, 25, and ceiling sashes 29-32 are installed at the tops of the columns 22-25 so that a frame construction having a sturdy shape-retaining rigidity is achieved, to which a rust-preventive coating is applied. A coated outer board is made of metal or synthetic resin which has been coated in different color in the coating line provided separately from the assembly line and is attached easily from the outside by bolts 5 to the chassis constituent body 2. The installing works of components 6 to the chassis constituent body 2 can be performed independently of the color changing works for the outer board, which enhances the easiness and effectiveness of the works.