To provide a connection box of a decoration duct by which its design and manufacture can be facilitated, the manufacturing cost can be reduced, and the inventory control stock can be facilitated.

A flat prismatic or a flat cylindrical box body 8A whose four duct connective opening 16 opened in cruciform four directions is formed at the side face is provided to form a decorative duct connective box 8 connecting the decorative duct 7 from four directions, to form piping lines or piping passes in the inside, and fitted to a forming part of an opening 16 for connecting ducts. In this way, a fitting part S of an opening member 18 altering the duct connective opening 16 to an opening with a shape or dimensions corresponding to a connective objective decoration duct is provided in at least one of the duct connective openings in a formation section of the four duct-connective openings 16 in the box body 8A.